Some freewheels like yours will have sprockets that may come off and turn around, providing a fresh (un-worn) surface for the chain to pull against. The end sprocket will probably have a built in spacer but can be unscrewed with a chain whip (it could be very tight). The 2nd,3rd & 4th sprocket are just plain thickness with a plastic spacer and may slide off the freewheel body and turn around if the splines on the sprockets are in the same location. As this is an old freewheel design you don't have shaped or profiled teeth or ramped sides to worry about - the sprockets are effectively the same whichever way they are fitted. You can do the same thing with earlier UG Shimano casssttes.
It's worth a try to get a few extra miles while you look for an alternative.