You didn't mention the mileage.

It may be time for a blow-down test. This will quantitatively assess the amount of leakage out of each cylinder and will allow to you determine if it's a bad valve (and which valve). You might need a valve job more than rings.

Before committing to a ring job, first look for a good used motor. I have a '91 B230F engine (Rex-Regina) and AW71L tranny in my garage that I bought as a unit for $100 with only 140k miles.

You can find 'em -- they're out there, though maybe not quite that cheap.

Here's a quick trick:

Tomorrow morning, with the engine stone cold, start it and let it idle for 15-30 seconds. Then shut it down and feel each of the four exhaust headers.

The coldest header is the one with the least or poorest combustion.

--
Don Foster (near Cape Cod, MA)