Thanks for the replies Papa and GeneH.
I have tried contact cleaners but maybe not enough or the right one. I will give your suggestions a try on the two motors. I have some Caig DeoxIT Fader cleaner and Faderlube I normally only use on stereo equipment as it is pricey stuff but I may have to give it a shot. I have been using CRC contact cleaner but not drowning the plunger.
Charlie