the rear is low. there is a check valve in the rear to answer mike it also allows you to bleed the fluid. If it is dropping down over time then there is a leak somewhere. The sunroof unit, the white dial is the dial used to adjust the vertical lift and placement of the sunroof at stop. Very useful if you want to make any adjustments.
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)