Hello and welcome
I want to say I been there and done that, if the bike it's riding fine i wouldn't fuss too much about it, it's a old bike and there's more thing can go wrong if you try take stuff apart.(unless you have a bin full of spare parts and know how to wrench)
Learn that the hard way in the garage rebuilding cars, it's a investment of time and cash that often doesn't pays back.
if the money is tight(which is okay), i would just invest in a good bike shorts and helmet instead of tune up(given if the bike is riding "true")
set up the bike geometry and enjoy riding as much as you can