for my 190e 2.6 i also remembered my pressure to be at 3 while driving and around 1 when hot and sitting. After a while it started to stay at 2 while driving and never reaching 3 and went almost to 0 while in idle. I changed my oil, thinking the filter was plugged and voila. Now back at 3 and 1.

BTW i use synthetic also, so the sensor is reading it right.