psfred - please keep us informed as to the effect of rebuild of pressure relief valve on the low pressure reading. I have a 92 400e with 165K mi (M119 engine) and it has a 0 oil pressure reading when the oil is hot at idle. It also reads 0 BAR doing 75 MPH when hot. It is kind of thrilling. When the oil is cold it reads 3 BAR at idle. I diagnosed the problem to bad sending (sensor) unit since when I placed an analog pressure guage it reads 22 psig when hot at idle, but so far I have not changed the sending unit to fix the problem (placing the analog pressure guage did not involve any oil leak or need to drain the oil). I am waiting for the next oil change to replace the sending unit. I have been driving in this condition for few K miles. I use Mobil1 10W30 but will switch to Mobil1 0W40 on the next oil change.