I currently own a 23 year-old Jeep Cherokee 4x4 and to say it "has seen better days" is a bit of a understatement. Fortunately it isn't my daily driver but I still spend lots of quality hands-on time with it in my garage replacing, re-wiring, and re-welding various parts of it so I can take it off road on occasion in the California desert.
A (non-comprehensive) list of work done:
Rear main seal on camshaft
Floor pan rust remediation and weld repairs
Leaf spring replacement and bracket welding
Thermostat, fan, water pump, and cooling system overhaul
Exhaust piping/muffler replacement and weld repair
Oil filter adapter upgrade
Shock absorber upgrades
Spark plug upgrades
AC refrigerant system flush and fill
Backup camera wiring and install
Roof insulation install
Brake pad changes (disc and drum)
Various oil/fluid changes