Have a clicking sound? Dump-valve seals gone bad? 600 buck you say? Pity you don't live in sweden, i would really like to take your money...
Here it is, in technicolor:
Changing 930 dump-gaskets, pictures galore
It's really quite simple job that can be done home in the garage. Save those 600$ (and probably 300$ too) and buy me a beer next time you are here :-P
New seals cost me 6$40c a piece....that's 13 dollars plus two hours of lazy wrenching and snapping pictures as i took everything out (never did it before)
Also, i had problems with fast idle that happened to go away after i changed seals and tightened all hoses.