The safest way of dealing with rust on steel discs of any sort is to
use Evapo-Rust (Ferro-Solve in the UK).  This liquid lifts the rust off
leaving good steel virtually untouched, apart from a slight blackening.
This avoids the need for using any sort of abrasive.

The disc needs to be soaked in the liquid overnight, then washed in
clean water and dried.  To prevent further rusting a light coat of
flexible lacquer should be applied (a friend uses "Harmony" hairspray
which is available in the UK).  This will not, of course, replace steel
where the rust has eaten deeply into it, but it is ideal for light
surface rust.  Evapo-rust is water based and pH neutral (i.e. not
acidic), so if a disc uses water transfers they could lift, but most
discs are OK.

This process was first described by Craig Smith in the MBSI Journal,
"Mechanical Music," a few years ago.

Regards,
John Farmer, UK