Electrical question (72 Olds W30 w/455)

[JOZW30]

Had this issue start late last season.

Car starts OK, but sometimes my "GEN" idiot light comes on and goes out after a couple of revs. It also occasionally comes on during the first couple of miles of driving after cold start up.

Usually when I am slowing down for a turn and I've got the clutch engaged.

Also, seems like the headlights are not very bright. No dimming up and down with engine speed (halogen lamps). measured 12V at socket with headlight switch on.

Battery is new.

Any thoughts?

Also, if I want to rebuild my original alternator, is it hard to do and where do you get the correct parts?

Thanks,
Joe