It`s the first time I actually hold one in my hands so here some pictures. (This is from the earlier 906s that had the piston in the clutch cover)
The combination of a needle and a ball bearing plus oil seal seems a bit over-engineered. The good part is it can be disassembled, checked, washed and regreased if ok.
The oil seal is a G 14-20-3 the needle bearing a HK0810 (8x12x10mm/ inner x outer diameter x width).
The ball bearing has 12 steel balls. The outer race is the piston itself (inner diameter 20mm) the inner race is the pin. So it can`t be replaced with a standard bearing. If it`s shot you`ll have to replace the complete piston with a new one (see P750 FAQ) or if you have the possibility you should be able to bore the piston to 22mm (7-8mm depth) and use a 608-2Z bearing with a new pin (see P750 FAQs as well). The needle bearing could remain inside and unused.

G.

Interesting stuff, how did you disassemble the bearing assembly? People can be ham-fisted at this so a few tips will help.

That's good stuff G. I just assumed the 906 was like the 750 in that department. Looks like I'll have to look around and start sourcing parts! Thanks Arch.

JW all there is is to lever out the seal, carefully remove the locking clip and pull out the pin. Some of the bearing balls will remain in place, others will stick to the pin because of the grease so one needs to be careful not to lose any.
I didn`t remove the needle bearing. I wouldn`t know how to w/o destroying it and the much bigger problem would then be to remove its outer race. (luckily mine is ok)
Assembly`s easy. Find a (clean) longer bolt that can be placed into the needle bearing first. Grease the needle bearing and the outer race of the ball bearing. Stick the bolt into it and throw the bearing balls inside. The bolt is just to prevent the bearing balls to fall inside the needle bearing. Remove it when the balls stick to the grease, push the greased piston back in while rotating it so all balls get in place. Put the clip back in its groove and press a new (!) seal in. Done.

Arch, no need to hoard clutch pistons. It`s not a problem to find the piston for a 748/916/SS/ST/Monster888/907ie etc which will work perfectly (it`s all in the P750 FAQs).

on my 750 and now on my 906 i replaced the balls with new ones (picked them up at a local bicycle store). also stuck the pin I my drilling machine at high revs and used waterproof sand paper to smooth the inside of the pin where the ball rolls, some new ball bearing grease and a new seal and it feels like new. No more squeaky clutch sounds

I was able to reconstitute the "over-engineered" piston (new meaning to the acronym "OE"?) that came with my new-to-me cover. I found several different places that carry the G 14x20x3 oil seal, in the US and EU. I needed a couple new ball bearings but still had a 608-ZZ bearing that failed in an old piston, and was able to salvage what I needed from that. I also took the V-grooved oil skirt off my previous piston and replaced the simple O-ring on this "OE" one. Just awaiting delivery of the new seal and I'll put it back together, and hopefully have the show on the road!