Fish box thru hull ?

[sidelock]

Just noticed the fish box thru hull (brass tube)on my 1975 18 SF is loose. There was mention in a thread a while back that there is a wooden block between the liner and the hull and I'm assuming the wood is wet . Has anyone dealt with this issue ? If the wood is indeed rotten how is it replaced ? Can expandable spray foam be substituted ? The present thru hull is a straight brass tube that is flanged on both sides, should it be replaced with a threaded thru hull fitting for a better seal ?