Hi Ricky
If your Keymatic is slipping and squealing on spin I'd be looking at the belt first off - the spin belt is the round section belt that turns the corner. The original belt is like rubberized rope, it works better than the modern replacements that are some sort of plastic. The modern ones are a bit stretchy, I think they can stretch enough to let the motor pulley slip. The modern belts are often red, they were sold here as "redthane" belts.
The way to check the clutch is to disconnect the belts (both of them) so you have the two pulleys free. Now rotate one of the pulleys clockwise, then anti-clockwise. Now do the same with the other pulley.
You should find that each pulley drives the drum one way, and free-wheels (doesn't drive the drum) the other way. Both pulleys should drive the drum the same way.
If the clutches work properly but are a bit noisy when freewheeling, you could use a tiny bit of machine oil to lube the clutches. Each pulley is the outer of each clutch, so to lube them just add the oil (or motorbike chain spray grease) to the inner edge of the pulley, where it slides around the brass centre. DON'T pull the clutches apart. There are irreplaceable tiny springs and rollers inside. The clutches are simple enough but the bits are tiny and the springs cause it to fly apart when dismantled.
Another cause of slipping and squealing on spin is bad drum bearings - and Keymatic bearings are weird. They are thinner than standard bearings, I couldn't find them anywhere. (I usually get bearings from bearing suppliers, not spare parts shops - cheaper and often better quality.)
Also the bearing mount I dismantled had odd brass shims and spacers in it, I couldn't figure it out. Too long ago for me to remember with any clarity, but I do remember thinking they are to be avoided.
Another source of noise on spin is the idlers for the spin belt - the small pulleys where the belt turns the corner. They get worn and rattly, can come good woth some grease on the centre bushes. The old cast iron idlers are indestructible, the later plastic ones wear out.
Chris
