My 42 Ford has a 6V starter and if you have a good battery and clean grounds the next step is to clean the commutator. They sell special stones for this.
The copper corrodes and creates resistance in the circuit. If my jFord sits for 3-4 months part of my 'pre flight' is to take the band off the end, put a stone on the commutator and bump the starter with the plugs out.
I have a write up
HERE Call the shop and ask that they clean them... and CHECK THAT THEY DID when you pick it up.
