I believe the cam adjuster does have to come off.
ToyCollector - I did up my K1'ish starter motor last year and my symptoms were slow and sluggish starting also. Found the brushes buggered to buggery-i-o. Brush dust everywhere. Easy to replace. New set from David Silver,..but I stupidly went to town looking for auto-electrical shop parts and ended up having a shop make a set for $75 - only to find them on Silver's 2 days later for about $10!
The cam adjuster removal can be tackled..have no fear, although I was nervous as well. I resorted to a trick I read on a thread here for re-adjusting the camchain and I have used it twice since. That is to insert a shortish stout allen key up the open end apply subtle pressure on the internals as I stab the starter button repeadedly WITH THE KILL SWITCH ENGAGED SO THE MOTOR WILL NOT FIRE....the allen key pushes in and out and when u feel it to be in to the maximum,....hold it with reasoned pressure while u tighten the locknut up tight. Works. Easy. U must not force the chain tighter than it naturally wants to go - so the pressure u place on the tool is merely containment - not forcing it inwards.
Regards
Mark
PS: Getitng the motor out of it's bay is a bastard. Not technically challenging but frustrating. U have to wiggle, prod, lever, shake and swear at it. It has to be de-engaged from the clutch starter gear..and it likes it there!