Hi,
do NOT put WD40 any where near motor bearings. It is primarily a Water Deterrent and is silicone based. It is not a lubricant. It will not mix well with any residual Hydrocarbon based lubrication and could well affect the lubrication qualities of whatever amount of the original lube which is still there. Bear in mind that sleeve bearings are sintered. They are full of voids which are there to hold the lubricant in close contact to the moving parts. If you have sprayed the wrong liquid at it, the liquid will SOAK into the bearing and you will NEVER be rid of it!!!!!!
I would not go for motor oil either as there are additives which are of benefit to an internal combustion engine which do not apply to electric motors.
As I have mentioned elsewhere on these forums. Lubrication should NOT be taken lightly. Especially when dealing with Capstans. Any recorder, no matter what the build quality, is only as good as the rotational speed performance of the capstan and associated mechanics. The electronics could be the best in the world but bad Wow and Flutter figures will kill it.
Good quality lubrication is easily available and worth the expense.
GPS16