Voltage regulator failure?

[CharlieO.]

Cruising back to our slip today I noticed the amp meter reading close to what my alternator is rated for(51a).
My USB plugs that also read voltage were at 17.5 volts. My DC2DC charger was reporting 17.5 volts feeding it.
I backed my RPMs down for the final 20 minutes to the slip and the voltage dropped to 17.

I immediately went to the engine room to check my batteries, they were not Hot and not showing any sign of distortion.

I am thinking it is a failed voltage regulator, does that sound plausible?

 

[SteveK]

sounds plausible

 

[Comodave]

That would be ny first guess too.

 

[CharlieO.]

Shopping for a replacement regulator, how do I determine if I have a short keyhole style case?

Voltage Regulator 105-64, 8RG2010A, R7-1 For Motorola / Prestolite MR/8MR Series with Short Keyhole Case Style - 8010197​

Can anyone point me to a replacement regulator they have used, or an economical direct replacement alternator?
I have the original style Motorola MR2018K (51amp) alternator on my Ford Lehman.