Over thinking the heater fan

[Delta Whisky]

First the background: smelled something burning while in flight a couple of days ago. Turned out to be one of the heater fan motors. (With about 45 minutes total time on the fans; so a fan respected for better reliability is in order.) Should be no problem replacing it - right? Well, not so much. But I have started the journey.

First issue - it appears that 1.5 inch (high) computer case fans are no longer made. That alone pretty much drives the decision to replace both fans - otherwise the mounting process becomes noticeably harder.

Second issue - it appears the available 12V fans shouldn't be run at more than 13.2 - 13.3V. Maybe driving a 12V fan at 13.9 volts is what did mine in - don't know. But if it was, I'm destined to smoke the second one and I'm not sure my heart can take another similar event. That helps me make the decision to replace both fans.

Third issue - by a rough estimate, about 90% of modern fans are of the PWM variety.

Forth issue - computer case fans are basically one of two varieties: standard and "high pressure". "High pressure" in home-assembled computer language means: able to push more air through a heat exchanger. (I'm so out of touch that I didn't know modern, home computers contained radiators and cooling fluid. What's this world coming to?)

Clearly I'm looking for something reputed to have a much better MTBF, is of the "high pressure" variety and is a direct fit back (120 mm) into the plane. It would be nice if it was reliable at 14V but that doesn't appear to be possible so:

Question one: what is the simplest, modern voltage control circuitry? Is it still the LM305 voltage regulator?

Question two - can someone confirm my suspicion that a PWM motor can be run full time at its nominal voltage?

I've pretty much found the replacement fan but would like the PWM answer confirmed first.

Update - Question three: If I'm reading the LM305 data sheet correctly, the input-output voltage differential needs to be 3.0V. This means it won't be a suitable answer. What would be a better solution? (Or, am I reading the spec sheet right?)