Advice Buying 1999 500SL - soft top problem

[skybound]

Just tonight I went and test drive an absolutely immaculate 1999 SL500 with 78K miles. I have looked at quite a few SL500's over the last few months and I have read a lot here in the posts on what to look for. I tried everthing in the car (including the air conditioning) and then took it for a test drive. When the test drive was over I had the salesman help me take the hard top off and then tried to raise and lock the soft top. Everything seemed to work fine until the rear of the soft top was about 4 inches from the rear locks and it seemed to stop completely, there was a humming as if it was trying to lower itself into the rear locks but after several failed attempts to lower and then raise and lock the soft top the results were the same, just a humming when the rear of the top was about to lower completely into the rear locks. I even had the salesman try to assist the rear of the top down into the locks but it did not move more than a half inch or so. As far as I can tell it seems that maybe the haydraulic fluid may be low (not sure but I believe the mechanism that actually moves the top is hydraulic, but I could be wrong), that brings me to my next question. If the hydraulic system is what moves the top and the the system fluid is low that indicates a leak somewhere. The salesman told me he would have it looked at and give me a call. Any advice on what to look out for when I return to look at this beauty of a machine? I ran a carfax on this car and it has only had one owner and even though I did not look at the records myself the sales manager told me that the car did come with complete service records from the previous owner. I guess the most important thing here is any advice as to why the problem with the soft top occured and if anyone here knows what I should look for when I go to look at the car again. I don't want some mechanic pulling a fast one by filling the hydraulic reservoir when there is a leak; if indeed this is the cause of the problem. Any advice here is appreciated.