Steve - I don't have a scanner that provides that sort of data - Just an Innova (equus?) code reader that does show which of the monitors have run and cleared, but this not work with continuous monitors.

I had not realised that the film type of MAS did not have a cleaning cycle. (BTW, my car is a '98 E320). The sensor has a flow through section with a flat shiny metal piece inside - presumably this is the hot film? Then below that, there is a dead ended cavity with some type of element inside - what is that?

I did check the resistance and voltage at my MAS - 4060 ohms at 8C and 5.02v supply voltage.

In industry, flowmeters of this type are commonly used - these units are in the $6000 range, so they don't throw them away - They do maintain them by removing on a regular basis, cleaning and recalibrating. This is what led me to try cleaning. Some type of ultrasonic cleaning may be what is really needed. Presumably Bosch have a method?