1980 240d alternator troubleshoot

car wouldn't start, pulled voltage regulator, inner brush was worn out, while outer was over 1/4 inch. both were worn with same concave profile. does this spell alternator trouble?
i installed a borrowed voltage regulator, and all seemed ok first day. now, at idle, if i turn the lights on, it changes pitch of the engine. the engine bay is clean, and alternator looks newer even though the car has way over 300k.
if i replace alternator, what amperage would i use(may install veg kit at some time w/electric heater. car has new battery and new bosch starter, but it seems to take longer to start than it should--the new battery was drained by the bad v. regulator--its now charged again. so would you recommend new alternator, or , just a new voltage regulator??
thanks much.

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