Sigh... Define "PROPERLY CHANGED" (as in - What engine? What OCI? What type of usage?) Maybe you can think for a bit and instead basing oil - do some testing to find a real reason?
It is possible that *oil* caused sludge, but very-very unlikely under non-severe usage.

Im sure it had nothing to do with the owner opperator. It could only be motor oil. whats the specifics defining your comment properly changed. deciding to change the filter as well, every 3000, reading the dipstick for advise, not actully doing it yourself as if could be done by a professional oil changer. Your comment only suggests that you didn't because you felt the need to include it in your brief opinion.