Re: broken skeg
I bought a boat last year with a 115 Merc on it and someone had replaced the skeg with a plastic glue on replacement, I wasn't fond of the idea at the time, but it's been fine for over a year. I think it said Blackfin on the side. It was installed with resin or epoxy over the remaining portion of the skeg, it looked like it belonged and I wouldn't have even noticed it if the seller hadn't pointed it out. I sold the boat and motor but the new owner is still running it with no problems. It actually seems to be tougher than the original, and I suppose it would take a pretty decent shot. It's also not so rigid that it would damage the lower unit if you hit something. The more I think about the idea of having a plastic or composite skeg vs an aluminum one or one made of stainless, the more I like the idea. The one I had on that one motor can be found here, but I have seen other similar product advertised too, blackfinskeg.com
I have also repaired a few less seriously damaged skegs with Devcon Aluminum putty. One of which is on a 70 HP that I own and has been fine for at least 5 years now. That one had lost about an inch off of one corner, I simply built it back up, filed and sanded it to the correct shape and repainted.
Yours sounds far beyond the latter repair.