Agree/disagree.
I agree that the head should be checked and properly scrubbed. With enough layered oxide, there can be an almost total blocking of the record function.
Slow RW/FW, I'm sorry isn't the belt, as it's servo driven. The RW/FF servo adjustment can be "juiced up" to run faster or slower, and the tension arm position also plays a minor role in the balance of the servo system, which in turn may affect RW/FF speed. In general, the centers of the tension rollers should "intersect" geometrically with the bottom edge of the tach/idler rollers. If you can't eyeball that, consult the manual for diagrams.
Third, with the added symptom of "squeal" it leads me to believe more in a common cause, that is the tape. If any single tape begins to shed, not only will the RW/FF become sluggish due to friction, but it may interfere with normal Play forward motion of the tape. Also, if the tape's shedding that badly, it could squeal as you described, and could leave a thick sludgy layer of oxide on the head that you'd need to scrub off with concerted effort. That would tie all 3 symptoms up with one cause, and the tape path should be cleaned and scrutinized, as well as sourcing a brand new reel of tape for testing.
Lastly, I'd be somewhat concerned at this point that the tape may be threaded incorrectly, in an orientation that is presenting the back side of the tape to the heads, which doesn't record very well at all, and ultimately sounds like you describe: very dull and hardly any signal.
So, that's 4 things to check:
Tape threading/correctness
Tape quality/shed
Tape head & path/cleanliness
Possible servo adjustments, (after everything else has been covered).
