If a voltage regulator is bad will it just quit working or can it work sporadically?

Other day my tach was dead. As instructed by a search on here I pulled the harness off and started the motor held red lead of my Fluke meter on purple, black on black. Got 1 to 2 volts which told me it was probably bad. Put it back together went to lake 2 days later. Tach still no workee. Voltimeter in dash and on Garmin 240 reading about 12.3volts. I know it should read about 13. Back at ramp ready to load 'er on trailer, look down, tach works fine. Rev it up a little tach works. But I honestly think my regulator might be shot.

Just want some thoughts before I park the boat and send off for another credit card to buy one. If that is the case, I'm pissed I have to go on vacation next week and spend my boat repair money.