The odometer is easy - it's a cog that disintegrates - kits are on Ebay to fix - a bit fiddly but do-able.
Re wiring loom in gearbox - this can happen when solenoids are changes and the insulation on them gets damaged (it gets brittle with age)...usually they move the wire so it's not near metal or replace the wiring (costs$).
Otherwise it's easy for the connector to the gearbox getting damaged if going bush so check that. Also disconnect the connector and cleand and tighten contacts. Remove codes finally and see if they come back.
Good Luck.
"If anyone disagrees with anything I say, I am quite prepared not only to retract it, but also to deny under oath that I ever said it." --T. Lehrer
"The secret of success is sincerity. Once you can fake that you've got it made." -- Jean Giraudoux