1977 450SL Starter Solenoid Needed

My 1977 450SL starter became intermittent. I removed it and found the starter to be in excellent condition, however, the solenoid does not
always conplete the circuit to the starter motor.
Any Ideas as to where I might find a new solenoid? Complete starters seem readily available, both rebuilt, new and used. However, I cannot find a solenoid.
I would also like to replace the motor brushes even though they are not yet totally worn out. As long as I have the starter out it would be foolish not to replace them because they are about eighty percent consumed. The commutator looks good.
One set of brushes is an integral part of the field coil assembly with no apparent method for replacement. Any Ideas on that? I would guess that one could cut the wire and solder a new brush onto it.
Thanks for any help.
Leonard Stearns Boise, Idaho
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