Mach 1, I was just wondering if you ever use injector cleaner or you just throw your injectors out when they get clogged? Yes, of course there are gimmicks like Slick 50 or Prolong, but there are also real treatments that can help clean an engine. Marvel Mystery Oil is one of them. It's been around for a long time and actually does clean the engine out some. If you change your oil every 2500-3000 miles it shouldn't be an issue, but some people just don't do that or the owner before them didn't. It's something that you should get an oil change right after, too.
Old Guy is probably right, too. For all you know, the sludge is what's holding the engine together.
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351W 89 Mustang GT Convertible