The parts to repair your heater are widely available. It's easy to do yourself. I purchased a new heater core assembly from Classic Truck Parts.
12v motors are available to replace the 6v motor.
For rebuilding services for just about everything, contact Then and Now Automotive. Call them. Website isn't really helpful. Also contact Atwater Kent for your capillary tube.
Then and Now Automotive
447 Washington St
Weymouth, Ma 02188
Ph: 781.335.8860
Fax: 781.335.1925
https://www.thenandnowautomotive.com/auto-parts-storeTemp sending units, coils, fuel sending units, tube radios, 1920s to 1970s (mostly 30s, 40s, 50s)vacuum advance, voltage regs
Atwater Kent
12 Jacques Street Worcester,
MA, 01603
(508)792-9500
http://www.mykmlifestyle.com