Hi Darren

I have been working with the 1550 for 10 years and we have 75 of them and have never seen a heparin motor fail.
Things I have seen fail are -plunger switch,end of stroke switch and poor solder connection for the plunger switch due to overtightening of the switch nut.
On rare occasions the PC10A has failed.
Check for dirt or debris on the worm gear and that the motor mounts are NOT tight.Also check the integrity of the carriage assembly.
I hope this helps.