Ken, I have little or no respect for oil additives as a solution to problems. Things that are worth having, have already been adopted by the oil manufacturers and have become necessary oil ingredients to pass the automotive tests (SF, SG etc.) That is not to say that new oil additives are not being invented: I'm just saying that the ones marketed as individual products are often valueless and sometimes simply frauds.
Generally, an old engine should run just as well as when it was new. If it doesn't, it can be fixed so that it does. Eventually, it may have so many worn parts that it is easier and/or cheaper to just buy a less-worn one instead. The difference between a professional and an enthusiast lies in when they think it is time to quit.
I'm glad your engine is running properly again Ken, it makes machinery much more satisfying to use when it works as it should.
