There are 5 hydraulic actuators in the SLK that operate the hardtop (2 open & close the trunk, 2 operate the top, 1 operates the latch which locks the top when it is up). The actuator in the headliner is known to fail and leak hydraulic fluid. If you continue to operate the top, the hydraulic reservoir in the trunk will get too low and the top will not operate at all. The fluid will sit in the headliner eventually causing it to wrinkle (and sometimes bleed through and drip onto the seats, causing damage). If your headliner is wrinkled and it feels oily to the touch, this is your problem. You must rebuild the cylinder (kits available online) or replace it. Replacement headliners are available for approx. $200.