WK713. It is the right spin on filter for your car. It is right next to/behind the power steering pump. It is better to fill it with diesel first but you can also hand pump it with the pump next to the IP.

The primary filter ( clear one ) is normally 3/4 full. There is an air bubble inside and it is normal. If it is dirty then it need to be changed. If Pepboy do not have it in stock then you can make do with squirting some brake cleaning fluid inside and give it a good shake. Pour all the crap out. Do it couple of times and it should be OK for a while.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.