"The front lock elements... is the cause of most hyrdaulic R129 soft top problems!" See http://www.peachparts.com/shopforum/showthread.php?t=35007

The lock elements are inexpensive and easy to replace. You can do some basic troubleshooting which may confirm the front lock elements are the source of your trouble. I have the diagnostic manual for the convertible top system and can assist you if you like.