The thrust pad is intended to reduce motor noise transmitted into the plinth. It consists of a nylon cup pushed onto the bottom bearing, inside which is a spring with a nylon button that pushes against the bottom of the motor shaft. The motor itself doesn’t have a thrust bearing as such. It shouldn’t make any difference to the speed. It’s not unknown for the whole thing to fall off! Whilst you’ve got it in bits, a drop og sewing machine oil on the bottom bearing wouldn’t go amiss. If possible try applying a drop to the top bearing too with a needle. Needs a steady hand…