I’ve never had one go manky? Are you definitely using the correct fluid grade/type?

 

Yep. I use Dot 4 and it has Dot 4 on the lid - including the new lid and screws that come with the replacement gasket. Apparently it's a common issue according to Thumpertalk:

swollen clutch membrane

I've notice my clutch membrane had been looking bloated, and actually wont fit correctly in the master any more, also saw black bits of rubber in my master cylinder. Not only bloating but evidently disintegrating also. Old one on the left new on the right. 2015 500 It sux that you cant buy the me...

thumpertalk.com

 

New one on me ...... l use 5.1, but same chemical shizz.

 

Definitely an odd one that. I’ve never had one go odd but have seen it happen when wrong fluids been used. You have used what’s recommended so it’s very strange. Even my 2004 RFS hadn’t gone manky but that used the mineral fluid not dot 4.

 

When the first one ballooned I suspected that they set the bike up wrong from new at the dealers because the o-rings in the slave cylinder also broke down, but now the new seal is going the same way, and the entire system was flushed and rebuilt when I needed to re-build the slave, I do wonder what's going on. I noticed that the bikes that seem to have the problem on that Thumpertalk thread are also 500's. Maybe there's a problem with the spec'ing of the part for the 500 on the KTM parts list. Maybe they've put a mineral oil gasket with a DOT 4 lid. Odd. I might try ordering a new lid/gasket for a different exc with a DOT 4 clutch system, see if it helps. I'll have a look see what's on other riders' bikes out at the track tomorrow.

 

Mine went out of shape and warped on my 2015 300 EXC. That always had good quality DOT4 fluid.