how to fix mercury 50 2-stroke dilema?

mate has a 50hp mercury 2-stroke (oldish model) that a mechanic says has a sticking valve(guessing powervalve?) that stops it from idling and once on water underload does not make smooth power.quoted him appx $2000 to repair.
any ideas if this sounds right
hammo, November 2010


done
expensive

GHOST, November 2010