Not 100% certain on your application, going on CLK repair work. On the CLK there is a rod between rear seats that you use a special tool to unlatch the forward trunk cover piece. Sounds like the cylinder that latches that is leaking so bad that it does not release. Find tool and pop forward trunk cover then go back to switch to see if system will continue sequence. Continue to ck reservoir fluid level and add as needed. Once it completes that cycle (all way open/all the way closed) continue to do it for about 4 cycles to get all air out.

If one cylinder is leaking plan on going thru all of them.

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Jim