First, buy the service and parts manuals from
www.victoryglass.com# 70-3332 (a.k.a. # R-384) Rowe TI-1 Service Manual, 122 pages $35.00
# 70-3333 (a.k.a. # R-385) Rowe TI-1 Parts Manual, 70 pages, $25.00
# 70-3334 (a.k.a. # R-384A) Rowe TI-1 combo package deal, both manuals above just $52.00
Those are not cheap photocopies. They are actual offset printed and licensed reproduction manuals with crystal clear photographs, lay flat binding, and laminated covers. Fully authorized by the original copyright holder.
Now to your speed problems. Many times it's a two-fold problem. The first being that the rubber turntable motor mounting grommets are compressed and now shot. This causes the entire motor assembly to either sit cock-eyed to the turntable inside rim or cause uneven wear to the rubber surface of the idler wheel. The second is the idler wheel itself being either glazed over/dirty or just plain worn down too far to grip the inside of the turntable rim.
To inspect/check in there, simply just grab the turn table and lift it straight up about 4 inches and it comes right off. Naturally do this with the machine unplugged for your own safety. Clean the inside rim of the turntable with a rag lightly moistened with Lacquer Thinner. That will remove all the crap built up over the years on the surface.
Victory Glass sells the idler wheel and the turntable motor mounting grommets.