I wouldn't go and start splitting cases yet.

This is an issue (as you mention) where
the aftermarket sprockets are a bit thinner
and don't hold the spacer tight enough so
the seal and o-ring leak.
There is a huge thread about it on thumpertalk.

I start by buying #33 & #35 and use the stock
sprocket (not teeth count but thickness).

Make sure you are not running the chain too tight either.

 

I put some silicon on the front edge of the spacer careful you don't put it on the seal then refit the sprocket. Make sure you have a tight seal when you refit the c clip ,if you don't it will leak cheers Adam

 

Thanks for the input.
Bajadog, I have already been down that road, the leak subsided a bit but still leaked. Aj300, I never thought of your solution.

Went to the dealer today and we both came to the conclusion that the front countershaft splines are wore out because the sprocket has a 1-2 mm rock to it with the stock spacer and o-ring. In lieu of replacing it it went with a 19.5mm x 3 thick o-ring, it's a smaller diameter but thicker than stock with the hopes this would provide the back space pressure required to keep the o-ring tight to the backside of the bearing. This appears to have worked and will wait to see what the longevity of this trick will be.

 

Glad you had is sorted out.

Why would the splines wear out (asking because my Berg is basically a KTM engine)?

 

6 year old, lots of BRRAAAP I guess. Been averaging about 200-250 mi a month (practice) the last 2-3 years, plus D36 scrambles.

 

Okay that makes sense. I guess racing would be harder than just my trail riding.

 

FYI, I have always replaced my drive system (f and r sprockets with a chain) from OEM to all Sunstar components. The Sunstar f sprocket is a copy in thickness to the OEM sprocket. I use the MXR1 chain and Works Z stainless steel rear sprocket. Even if I use the standard steel rear sprocket, the longevity and quality of this system is far superior to others on the market.