If it's an old unit it COULD (Not is) be the belt drives have stretched, when it's under pressure (the tape) it slips/drags and is not worth repairing even if you could get the belts.
You could try a tape recorder head cleaning tape which you insert and it cleanes off the heads. About once a month you use them. If it is belt driven you will have a hell of a job getting the belts, even rubber drive collars if that's the type.
Or renewal.
Try a local car accessory shop they may be only to pleased to fit one of their units free of charge, may cost a little more because they can't buy in bulk like the big boys can, but you do get the service. As your on the net search the Halfords web to see their prices and units. then decide is it the local man struggling to make ends meet or do you go to the big un who's got more money than you can 'poke a stick at' and who may charge for fitting the new one.
From an almost 65yr old who took time at 48 to build a porch....only 5yrs.
Bob 64yrs 11 mths, October 2005