Greetings from RojoLand!
Rubber rejuvenators are a temporary solution at best. No harm to use them, but the real answer is to replace the rubber parts.
(Teac AR-40-S? That should be RA-40S, which is the record preamplifier unit on the A-4010S machine [I have one too]. It is a bit odd that the amplifier's model number is more prominent on the machine than the deck's, which appears on the head cover.)
Take care,
—
J. E. Knox "The Victor Freak"