Re: What is the best "High Gloss" sealer? Resins, Varnish, Clear Coats?
The reason it's yellowing is because the varnish itself didn't get a good bond with the wood (it lifted and moisture got underneath it). I fought this same battle with a boat I refinished a couple years ago. Sanded it down to clean wood, did all varnish per the directions (8 coats) and it lifted before the end of the year. 2nd Time I refinished I stripped it again, used a chem stripper to pull out anything that was soaked deep into the grains and re-varnished (8 coats) and it lifted the following Spring. 3rd time I re-did it stripped, chem clean and did all my base coats with west system (2 coats an hour apart no sanding between ** MUST USE THE 207 HARDENER), let set up overnight, sanded with 220 and applied 2 coats varnish (sanding between with 400 grit) and no problems. The epoxy bites onto the wood much stronger than the varnish. With the total of 4 coats (epoxy and varnish) there is actually as much depth or more than when I had 8 coats of just varnish. At that point I was sold on the process. Much quicker, less sanding and longer lasting results. varnish maintenance should be a once a year or even every other year maintenance (light sanding and a fresh coat of varnish). If you haven't done so already you can see how it looks on my video (link below in my signature).
Good luck!~