Re: aluminum vs fiberglass
The '65 18' Starcraft I/O that I completely restored had sat half submerged in a marina for many years. I found that the transom was damaged.
It was a simple matter of removing a few rivets and some thru bolts and out with the old and in with the new....while the engine was out of the boat.
The biggest problem was finding (and paying for) 3/4" marine plywood. (Used 2 layers for those interested and loaded it up with linseed oil).
You can do a quick test with your knife. Usually on alum they are exposed and a gentle stabbing here and there will quickly tell you if the wood is good or bad.
Other thing is that the transom is out in the air and usually off the bottom so you don't have the same type of problem with transoms you have with stringers.
And no, I know of no aluminum boats ever produced with wood stringers.
Mark