Metex - M3850D - unstable higher resistance readings

[iMo]

I've been using this nice meter for almost 30y and it works fine except the resistance values larger than ~kiloOhms are getting unstable readings (something happened a month ago or so)..
Most visible it is with large values where it takes pretty long time to converge to an aprox value and even then the readings are unstable and a touching the resistor's leg makes the reading almost all over the place.
Perhaps somebody has made the similar repair already, I've found the schematics (1995) online (attached).
My suspects are the two MPSA42 protection transistors around the ohm ranges coming into the MAX134..

[iMo]

Added the "service manual" with pcbs..