dimed lights and corrosion

Depends on who/ what "tested it." Maybe, maybe not

Don't just jump on the regulator, either. I've posted before some of what causes ovecharging. Part of it can be voltage drop on the positive side of the harness feeding the regulator (voltage drop on the entire path from battery--through the firewall--to the ignition switch connector--through the switch contacts--back out the switch connector--back out the firewall--and finally to the regulator)

Ground---the entire path from the regulator--bolted to firewall--grounded to engine block--grounded to battery.

About .2V (two tenths) voltage drop in either path is too much, and the charging voltage goes up as the voltage drop goes up

And of course, it CAN be the regulator.

I would not go out and spend money on a (especially expensive) new battery until you get the problem in hand