By "brew lock" do you mean the "group head"?
The bit you lock the handle into?
If yes then AM will tell you youve been overdosing.
Which basket do you use and how far from the top is the coffee after youve tamped it?
I dont think its unusual.
I had one replaced a year ago and the new one could do with replacing soon, however it is used more than your one.
P.S. *They dont have a boiler. Did you mean thermoblock?
P.P.S. Did Sunbeam tell you which agent to take it to? Only some are trained/allowed to repair the 6910.