I would personally try the Slick 50--the High Mileage version. If you have access to a compression tester, it would also be a solid idea to take readings before and after.
The tricky thing with engine issues is that (obviously) you never know for sure what the problem is...until it's fixed. And sometimes the answer can come from wa-ay out in left field. In 1968, I had a 1960 Chevy with a 283 V-8 which blew up entirely in the middle of the night (on the highway). Lost power, engine died, clouds of oil-smoke everywhere. Dead beast.
It turned out the clip that holds the distributor in place had broken in half. The distributer jumped up, went absolutely out of time, and...!
Literally took one penny to fix it. Stuck one edge under the retaining bolt, the other over the distributor edge, cinched it down, and it was good to go. Ran it that way for many more miles before trading it in.