this could be a big one.
first, the broker is probably full of it - he's got a personal stake in the sale
so his opinion is next to useless. you need a good engine guy to take a look at the coupling where the shaft mates with the transmission
and probably the transmission
as well. then there's the packing gland
. the vibrating shaft may have put the gland out of round or worse, loosened it, and it will soon become a source of leaks
. it is likely damaged by the extreme vibration of the shaft. you need someone to look at the whole drive train.
is the cutlass bearing in a strut or in the hull
? if it's in a strut then look for strut damage - you might need to reinforce the hull
where the strut is attached. if it's in the hull see if it's loose. if it's loose, than you may have to rebuild
the hole that the cutless bearing goes through.
if it's just the cutlass bearing then you're maybe looking at a $300 job. if there is any additional damage, and it's very possible, i think i'd tell the broker you want at least $1000 off the price