Working from memory here, but I think the kickdown solenoid has a crush washer, plus a small o-ring at the tip. The banjo bolt through the solenoid is a 19mm. Try gently snugging it up. I seem to recall the torque spec on that bolt was only in the 10-15 ft/lb range.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.