I just noticed this post. Recently my Milwaukee solenoid would not shut off completely/properly on my Apex, could have been the low voltage thingy (plus I cracked the plastic bubble counter). I can ship the regulator to you if you pay the shipping or can find a cheaper way to get it to you Brad.
I ended up replacing it with
this, its working well, I just had to buy a separate (with check valve) bubble counter. Aquatek has lesser models also.