Whats wrong with the original?
If the core isn't leaking you can either repair or replace the blower motor.
If it's the switch they are also available. Be advised that the aftermarket 6v rheostat type only seem to last about 3 winters, atleast in my case. They aren't too expensive and are very easy to swap out.
My original 6v heater didn't leak but the blower motor was frozen. I disassembled the heater, took apart the motor, cleaned and lubed it up, cleaned out the fins on the core and the heater can run me out of the cab on the coldest days if I run it on high. I'm still amazed at how well it works even considering it's age (1949).
If you just want to swap yours out several on-line parts houses carry kits in both 6v & 12v versions.
Good luck
Dave
