Sorry to hear about your troubles with the excavator Ralph. I've got about 5 hrs total run time on mine and all has been good. Cylinders dry and no leaks in the body. I did have my first hiccup yesterday. The relief jammed and suddenly had so much power the stick function pulled the whole machine like there was nothing to it! After it cooled down things went back to normal.
Anyway, I'm a little embarrassed I never noticed myself but after seeing your post, what the heck IS the 4th valve for?
I'm off to the basement......
Mario