DME Fault...

Have had my mechanic looking into misbehaving engine (1994 540 Auto). Using an ULTRASCAN controlller to talk to the on-board computer, Have identified and replaced Faulty AFM and am sourcing replacement oxygen sensors. Also getting a message of a fault on the DME. DME is currently 'chipped' (by PO with unknown origin). running has been ok but a little weak over the last 6 months and over the last 2 weeks has become unreliable, cutting out and needing the battery terminals taken off for 20 min to reset the computer to get to next stop (1 hour).

Is DME repairable / Replaceable?
Is the fault likely to go away when the oxygen sensor is fixed?
It the 'chip' a likely culprit - worth replacing??

Currently not running. need assistance. Thanks in advance