There's more than one metal valve. One of them looks almost identical to the Porsche plastic one. There is another that is all metal that does not have an external arm. I put this one into my wife's 968 4 years ago and it is still fine. I got it at NAPA.

Dan
'91 928GT S/C 475hp/460lb.ft

 

I wasn't able to find anything in stock at NAPA with 3/4" hose inlet. Plastic or metal. They show a metal unit for an Audi 100 (BK 6601410), but it seems to be out of stock throughout the NAPA network.
I have a metal one coming to me from AutoZone. It crosses with a '91 Audi 100. Everco 74671 . It's $20 delivered, so I'll see how it holds up.

 

Rock auto has the four seasons valve for $11.05 on closeout. P/N: 74671

Here's a pic.

 

Weird. Same p/n as the Autozone unit, but completely different valve. It's identical in appearance to the out-of-stock NAPA "Balkamp" that crosses for an Audi 100.
Both have the necessary 3/4" inlets. On the 944 board I read a post about one of our oem plastic valves opening up on the track and laying down a slick of coolant for the next guy. Metal seems like the way to go here...
....unless you don't mind the possibility of this happening:

 

The last plastic one I got lasted exactly 1 (ONE) freaking week! I knew then that I was going to have to go to something else.

 

Yup, that's the one I was talking about.

Dan
'91 928GT S/C 475hp/460lb.ft

 

OP, if you're still contemplating a replacement valve, I'd jump on this one from Rock Auto. This appears to be the same unit as the one at NAPA & other parts houses that apparently is out of production (why? that's a good question).
But for $11 plus shipping for a metal valve, you can't go wrong IMO. If you're more comfortable with the oem part, 928 Specialists has them..but considering the reported failure rate of the plastic ones, I'd keep a metal one around as a backup.

 

^^^^^ Only 5 left at Rock Auto...

 

Yeah, i ordered one from Roger a few days ago before all this "plastic vs metal" talk came about. I paid $20 and i'm expecting it today or tomorrow. I'm assuming its the plastic one. oh well. i'll throw it in there and see what happens. but you're right. i think i may buy this one too as a back up. for $11 you can't go wrong. question though... this is still vacuum operated, right? is that little thing sticking out of the top for the vacuum line?

 

btw - there's a bunch of these on ebay too for $14.54 plus shipping. just type "valve 74671" and they will come up.

 

No... only 3 left.

 

A word of warning - many, if not most, vacuum-operated heater valves open when vacuum is applied. The 928 valve closes when vacuum is applied...

 

These specifically stated that they close with vacuum.

 

so that's bad then. we need ours to close with vacuum, as Wally stated.

 

I'm sorry... I meant closes with vacuum.