A friend of mine asked me this a while back - I've still got the reply so have just copied & pasted it for you to refer to. I'm sure it doesn't cover
everything but it's a half-decent guide to go by for a noob.
Inspect every aspect of the lower body - it's pretty much all prone to rotting. Make sure you tilt the rear seats back and pull back the boot carpet back in its entirety - no other trim needs to be removed to do this. The soundproofing under the carpet often gets wet & kills the boot floor. VERY rare to find an original or un-repaired floor. Check rear cross member - a BIG expense repair & WILL fail a MOT. Front inner wings and battery tray are also likely to be roton.
Check every piece of electrical equipment - especially the electric windows. Also check rear wiper works.
If applicable, open both sun roofs - a lot are permanently sealed shut as a lazy fix. On this note, you'll be lucky to find one without a saggy headlining.
Check for leaks leaks in the engine bay - especially the steering box, vac-brake pump, fuel injector harness, rocker cover etc. Also check the diff seals and transfer box seal.
Check high/low range gearbox works - slide it to the left in both ranges to check the diff lock light illuminates on the dash - it should go back out again when you slide it back.
ABS light, if applicable, will stay on upon starting of the engine. This should go out when vehicle exceeds 5mph.
Check the rubber seals around the rear most windows & the tailgate window - these are prone to perishing. Also inspect windscreen seal as they often leak around the top, but it's an easy fix with some marine sealant or similar.
Check external door locks work on the key - these are prone to failing.
Check usual signs of overheating. The cylinder heads on the 300s are a bugger for head gaskets due to people not cleaning the radiator fins out. On this note - check the rad fins are not blocked or damaged.
Check it goes into 1st & 2nd gear ok. If it doesn't, this is a sign the gearbox is on its way out, as people neglect to ever change the oil in them.
Check the rubber coupling between the rear prop and the diff - these are often worn but it's a cheap fix. £30 for a new prop doughnut.
Good luck.
