Matt, the potentiometer can be bought seperately. Prices from $40-80. the picture does show the correct part. The part number is in my thread you found. I really do not think it is the pot. However, I am still think you have an ignition issue. However, it would be nice if we could see the eha and dutycycle numbers too. This may help confirm the problem is fuel or ignition.
m

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Martin Ingram
Colorado Springs
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)