Worked for me...

[OldRoller]

36 minutes ago, calw said:

the ideal valve

There are available small ball valves, 3 wire fully flow adjustable, built for external exposure, with minimal current requirements. Auto return to open or position maintained on power shutoff. Additional required device is a potentiometer for the position control, mounted on the heat control base, operated with stock heat lever. 

And cost less than a rebuild kit for the old heater valve.

A better mouse trap? Nah, I'll live with a stiff lever, broken valve mount, drips in the cowl... and it gets too hot I'll open the window.😎

[jimk]

1 hour ago, calw said:

Ideally have a variable position function- partially open for partial heat and maybe just a little bit open when closed (if BMW's tiny hole in the OEM heater valve was really necessary). 

I believe the constant flow (sometimes called Internal Bypass Rate) is not only a BMW thing.  Ford has a spec for their heater water control valves.  The reason is a bit of chemistry (users here that are chemists, help out).  In stagnant coolant the anti-corrosion additives become depleted in certain areas of the cores and pin holes develop there.  Also is the cause of aluminum pitting between the nozzles and hoses,  there is no replenishment of additives in that location from lack of flow.

[Son of Marty]

I've seen these Ford valves adapted to the 02 heater box there from the f150/250 pick-ups and are about 30 bucks from Ford probably cheaper on Amazon Etc.

 

[SydneyTii]

2 hours ago, Son of Marty said:

I've seen these Ford valves adapted to the 02 heater box there from the f150/250 pick-ups and are about 30 bucks from Ford probably cheaper on Amazon Etc

That looks like an interesting idea!