I'm an A4 believer.
They are dumb struck stupid (simple) little flathead motors that will run forever with very little care. (change the oil, keep the fuel clean, a coil every couple of years, file the points, and go sailing!)
before you consider replacing or rebuilding, have it checked out. Unless something is going clank-clank internally, It can be fixed to run reliably for years.
We are not primarily on earth to see through one another, but to see one another through
Some people are like slinkies: not really good for anything... but you can't help laughing when you push them down the stairs