Hotpoint Wm52 Final Fast Spin Problem

I have an old Hotpoint WM52 which has given up doing the final fast spin on any programme. The motor works and drives the drum normally during the wash cycle, but won't go up to fast speed for the spin dry. This started as an intermittent fault but has now become permanent.

The machine drains perfectly well - to be sure I cleaned out the drain filter and found only one small 5p coin in it (was hoping for a larger haul), removal of which has not changed anything.

I have changed the brushes on the motor - even though they were only changed a year or so ago and I don't use the machine heavily I could see some sparking when the motor turned so for the sake of a few quid (sadly not recouped by drain filter findings) I did it anyway. Sparking has reduced but still no fast spin (I'm assuming a small amount of sparking is normal).

I took the motor out to inspect it and noticed that the commutator on the armature looks to have worn down slightly, by less than 0.5mm, where the brushes contact. I took a small electrical screwdriver and ran it between the commutator contacts to remove any residual carbon, but to no avail either.

I have read elsewhere that a worn commutator could be the cause of the problem, but before I spend a substantial amount of money on a new armature/motor I would really appreciate some knowledgeable input on the likelihood of this, and anything else I might be able to try. Also, if this is a likely cause, would anybody be able to explain to me why the motor would work normally but not at high speed - is it simply a loading issue?

One other possible cause that has just occurred to me, although I admit unlikely, is that I appear to have mislaid a pair of underpants - unless we have a knicker-snatcher in the neighbourhood it is feasible that these have somehow got stuck between the inner and outer drums, possibly wrapped around the spindle, but drum turns freely by hand so we can probably discount this one... is it at all likely?

As I said it's an old machine, and I know they do not have a particularly good reputation, but I've had it nearly 10 years when it was given to me second-hand on the understanding that it was on it's last legs then, and I have grown quite attached to it. I like to keep things going as long as I possibly can.

Any help/ideas/pointers gratefully received and appreciated.