'03 SL500, '03 SL55, '97 SL320, (2) '91 300SL, (2) '91 500SL, '00 S500 -- all for sale
This may be a possibility. To discern if this is the case move the bow by hand while the roof switch is pressed and feel if there is hydraulic pressure trying to raise the bow.May be the issue is that there is not enough hydraulic pressure?
Reading fault codes may also provide a clue. If the problem is the REL15 relay that Swany mentioned, then I'd expect a fault for the bow not being raised.