Periodical cleaning of every surface in contact with the magnetic tape: heads, tape guides, capstan shaft and rubber pinch roller. Reel to reel recorder performances decrease dramatically when too much dust and oxide deposits are on these surfaces.
The picture below, from a Revox owner's manual, shows in black the parts need periodical cleaning. Usually you can reach them in easy way without dismounting any part of the recorder than the heads cover.

How replace it.

• The method can be different from a tape recorder to another one. Usually the pinch roller is set in its position by a screw and a washer. Using a non magnetized tool you can unscrew the screw to remove and change the pinch roller. Be careful avoid to touch the heads with the metallic screwer. At last don't forget the very thin washer, if present, when mounting the new pinch roller.

Although you are not a professional in electronic please read the following: you will find other interesting news.

The main thing in reel to reel recorder is the perfect mechanical contact of tape with magnetic heads surface. It has to be perfect to have a clear and high level output signal. The electronic circuits downstream have less importance than the upstream right mechanical aspect. This is why BEFORE any electronic alignment they have to check the right tape path, tension and speed, the brakes and heads azimuth and zenith angles.
Often this fact is underrated. On the market you will find many seller claiming the recorder is electronic perfectly aligned, but none words about mechanical! :-(

What to check. They can find on the market two reel to reel recorders same model, firm and aged: one is looking as brand new and the other one as taken out from a garbage dump! And good looking doesn't necessary mean best working.
Always I do these check step by step:

• BEFORE turn the recorder on I check its outside general condition, the wear and dirty of the external parts, tape guides, heads, pinch roller, check the fuse, the main plug and cord integrity and the right main voltage setting. 
• Next step I dismantle the recorder and check the inside general condition looking for burned components, the original lacquer drops on the calibration screw and the . . . dust! Dust can tell you much about the device. An equally spread dust means all the parts are original and the recorder is not a tweaked machine. I never trust in vintage device with none dust inside unless they said me the recorder has been recently cleaned and aligned and give me under warranty.
• Only when the previous check are O.K. I turn the recorder on, check the power supply voltages, transport tape, playback and record functions, and the absence of noise from the input, output and monitor switches.

What to do. It depends on the different problems I found before.

• If none big trouble occurred I just clean the recorder outside (and believe me some times this could be very hard . . .) to bring it back nice looking, clean the inside, demagnetize, check the mechanical and electronic alignment as per servicing booklet.
• Lubrication is not necessary for all tape recorders but only if required by the factory. I.e. Revox, Studer and Telefunken reel to reel recorders don't need lubrication. Oil could be dangerous if non requested. 
• The most common electronic faults usually are due to dirty switches, calibration trimmers (i.e. in older Revox machine they have to be always replaced), electrolytic and tantalum faulty caps and at last transistor or i.c. when you have background noise or distortion problems.
• Regarding the mechanical usually the parts to replace are bearings, brakes parts and rubber parts when present (belt, pulley, transfer, etc.).

I.e.: to have a Revox B77 input and monitor rotary switches W E L L cleaned is not enough a cleaning spray but it needs to completely dismantle the recorder to remove the switches from p.c. board.

RUBBER PARTS