The problem
When I rebuilt the caliper some time ago my fingers slipped and I pushed one of the 32mm pistons in at an angle. It was late and I was in a rush so I seated it correctly and refitted the caliper. Fast forward 12-18 months and I noticed a small fluid weep from one of the 32mm pistons. When I looked at my notes on the bike, it turns out it is the same piston. So I thought it likely I damaged the fluid seal and would need to replace it.
Single seals
BMW doesn't supply them, nor do BMW parts specialists. The people I spoke to said that Brembo make a number of different profile 32mm seals and that these ones aren't available. Being a sceptical person I found a 32mm seal supplier and ordered one to check the dimensions:
https://www.motorcycleproducts.co.uk/brake-caliper-seals-32mm-x1-p-264938.html. I measured them against the original seals I removed when I rebuilt the calipers (which I have in a box of old parts). BMW seal first, generic part second: ID 32.2mm, 32.0mm; width 3.22mm, 3.15mm. Height was the same. Obviously it's hard to measure this part accurately, but from what I can see they are not that far different.
Seal replacement
I replaced the leaking seal with one of the original BMW ones (two are badly stained from missing dust seals, but the other two were in decent condition). I would have liked to try the generic part to see if it the caliper leaked afterwards, but I was going out on the bike this weekend and needed it at 100%. The seal I removed as slight damage, as I suspected. See photo.
Brembo seals
Does anyone know definitively what is different about the Brembo seals from other ones? I don't think it's safe to use any old part, obviously. Also, I would like to know why replacement seals are available for the rear caliper but not the front.
