Recently I have had a number of issues with the convertible top on my 99 XK8 and have sought advice in many places in doing so I stumbled across Marvin (no not the paranoid android) he can be contacted on 1-888-317-9340, he is extremely helpful and also sells parts you might need, not only that but if you can’t fix it he will fly to your location and fix it (yes you do have to pay him) he is a lead technician and knows his shit.
Please note I have no affiliation to him I am just recommending him because he is very helpful.
Symptoms
The roof would open ok but when I tried to close it the roof would struggle and sometimes I had to try a couple of times, when it did make it the catch wouldn’t raise and therefore I couldn’t lock to top. Cure
I disconnected all the hydraulic lines and blew them through all but one (the line from the pump to the headrail marked ‘F’) this line was partially blocked and after spraying lots of brake cleaner down it a load of gooeeyy fluid came out, when I finally got it to flow freely put it all back together with nice new fluid and it works perfectly.
Apparently this is a known problem that the fluid turns to gel .