Just to update you on the situation: I replaced the spring today and everything seems to be fine. The screw is out farther than with the old spring and the pressure went to 12 bar right away.
The pressure goes up to a point, stays there for a few seconds and then begins to drop off slowly, with no locking up of the lever.
Thanks for all the input and help and thanks to Jim at 1st Line for his help, too.
Barry B
