Hello: I'm purchasing a 2008 Gl 320 CDI with 19" rims. I would like to purchase a second set of 18" rims with winter tires and place a second set of tire pressure monitors. What are the oem part numbers and do I need differernt valve stems?

Yes, you need the valve stems that match the sensors.

The sensors are at least $200 each.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles

The valve stems are part of the sensors. You can get sets of four for much less than $200 per sensor ($800 total).

for $500 at www.tirerack.com