It is fairly unlikely that you are going to be able to fix this thing.
First: All 8mm and newer consumer video tape formats use the video
signal for "tracking" adjustment. There is no "tracking head" or
"control track" as in VHS and Beta(max). There is no adjustment you
can make without a special wired remote control (RM95) or a computer
emulator thereof. Second, it is more likely than not that your problem
is mechanical. That is: The tape is not following the correct path
through the machine. From your description, it sounds like
more-or-less normal wear-and-tear...assuming you've cleaned the
mechanism...and not damaged it while doing so. Actually, your
description of the problem does suggest a thorough, professional
cleaning might help. This does not involve a "cleaning cassette", but
partially disassembling the machine and using the correct materials and
procedures (NEVER using cotton-balls or "Q-tips"...which can cause a
kind of damage to the video heads that produces exactly the effects you
describe.)

Overall...probably best to replace the machine with something a decade
or so newer.