New Third Brake Lens, Same Old Leak

[ktnez99]

For those who were at the December Shed at @t-tony 's you may recall my asking about the third brake light on my car's boot that is persistently leaking.

I bought a new lens (second since May) from BMW with a gasket and fitted the lens...poured water over the area...no leaks...me? Chuffed to bits.

My elation was short lived though and I quickly realised that the leak was still there.

My question is simple: has anyone any idea why this light is leaking rain and how I can stop it, please?

 

[Grumps]

If you've tried several lights and gaskets it must be getting in from another area, or possibly at some point the boot lid has been dented and straightened out but it's not 100%?

 

[mrscalex]

It’s been a few years since I’ve done one. In fact it was the first job I did when I got into Z3s.

But from memory they are very difficult to seat properly with the new style gasket. You have to be very persistent and use firm pressure.

Just a thought and I know it’s money but you may find a windscreen fitter is the best placed person to sort it, then they’ll have to guarantee it too.

 

[ktnez99]

If you've tried several lights and gaskets it must be getting in from another area, or possibly at some point the boot lid has been dented and straightened out but it's not 100%?

No dents @Grumps remember I know my car’s full history Thanks for idea.

 

[ktnez99]

It’s been a few years since I’ve done one. In fact it was the first job I did when I got into Z3s.

But from memory they are very difficult to seat properly with the new style gasket. You have to be very persistent and use firm pressure.

Just a thought and I know it’s money but you may find a windscreen fitter is the best placed person to sort it, then they’ll have to guarantee it too.

I may try re-seating it then Robert @mrscalex and see if this works. A windscreen fitter might get a call after this if my re-seating fails.

 

[Jonnysnapzzz]

For those who were at the December Shed at @t-tony 's you may recall my asking about the third brake light on my car's boot that is persistently leaking.

I bought a new lens (second since May) from BMW with a gasket and fitted the lens...poured water over the area...no leaks...me? Chuffed to bits.

My elation was short lived though and I quickly realised that the leak was still there.

My question is simple: has anyone any idea why this light is leaking rain and how I can stop it, please?

Did you get this sorted? I have the same issue. I fitted a new gasket without any luck.

 

[ktnez99]

Did you get this sorted? I have the same issue. I fitted a new gasket without any luck.

No, unfortunately. Been ok in the sunny weather - obviously - but now it’s back to seasonal April weather and raining. I’ll look later but know it’ll be leaking.

I suspect the actual bodywork aperture has been distorted.

 

[Mazza]

Sorry you are having problems with this Dawn,
If the leak is definitely coming from the 3rd light would it not be worth trying a clear sealant on both sides of the gasket when its being assembled ??

 

[ktnez99]

Sorry you are having problems with this Dawn,
If the leak is definitely coming from the 3rd light would it not be worth trying a clear sealant on both sides of the gasket when its being assembled ??

Thanks Malc. Yes, as a last resort. I’d prefer to get the aperture aligned correctly, tbh. It’s rather maddening and didn’t leak pre-bodywork being done.

 

[bessieblue]

On my caravan we use a non setting sealant for joining the panels bit like putty, that could be used to take up any gaps , it comes in a strip or in a tube for a mastic gun.

 

[Craig Machin]

I had the same issue when I fitted a new light and gasket.
I applied Vaseline petroleum jelly to the seal and all seems ok

 

[Dino D]

I had the same issue when I fitted a new light and gasket.
I applied Vaseline petroleum jelly to the seal and all seems ok

I used some silicone grease-works for a bit then washes out so needs reapplication.

 

[Mario]

Are you absolutely sure it comes through the 3rd brake light? I had a problem in my early days once where the boot lid would appear covered in water but the leak was actually from the aerial grommet, there was a void just under the rear left tail light that was filled with water which evaporated and condensed at night in the boot lid underside making it look like a 3rd brake light leak. Once that was rectified no more water droplets anywhere. You might have that or a similar problem if the rear of the soft top is not sealed properly and water is leaking on the boot. I would remove all boot carpets etc if you are not sure to determine if water is coming from another place. Before I discovered that I also tried changing the 3rd brake light and its very very fiddly you need to seat the rear back plate and make it click but it will detach itself a bit if you let go and you won't get a positive attachment until you have the motherboard with the bulbs pressing on the legs of the black backplate - the trick is to get someone to hold it firm from the other side while you or someone from the inside presses the black plate so it stays clicked in place and then pushes the motherboard and screws it back, another problem is - I would not personally screw the backplate to the lens "all the way in" reason for that is the plastic will bend ever so slightly *you can visually see it) and compress the gasket more at the screw points where in between you will get a sligth "bend" and uneven pressure being made on the gasket which is not good. Look at the red lens edges and once they are screwed in they need to look completely straight with an even (small) gap.

 

[Dino D]

@Mario
I took permanent action to solve the antenna grommet issue

Have looked at the same for the 3rd brake light - it doable just need to find a nice sleek led strip go on around the hood well...with the way LED tech is going there must be something that can be integrated neatly...better add it to the list