This is only intended as a guide of what to look for. The best bit of advice I can give is buy the best you can afford. There are quite a few cars out there in good condition and also some wrecks so be careful what you buy.

The Main points are as follows:

Exterior:
Check for cracks and crazing or flaking paint. A complete professional re-spray will about £2,000 to £3,000 and if you are going to tackle it yourself it will take a very long time to do it properly. Check the body for any irregularities like door gaps. Recent re-sprays can cover a multitude of sins so beware. SE5 models have metal reinforcements in the bodyshell which can rust and crack the body due to the metal swelling especially under the door treads on the sills. This is quite a difficult job. Cars can be fitted with Dunlop wheels, these are steel composites with alloy centres which can corrode each other and are next to impossible to restore. Other cars can be fitted with steel wheels and fibreglass covers or Wolfrace wheels which can be difficult to keep in good condition.

Interior:
The seats can break and also the ratchet for the tilt mechanism can wear and if the seat back is able to be pushed back on the ratchet this is an MOT failure.. The leather seats of later cars can be badly cracked and are expensive to get repaired. SE5 interior panels are made of a plastic that degrades under heat of the sun. The panels can be quite severely cracked but replacements are available. Check all interior trim to make sure it’s all there and not badly worn as some parts are hard to find. Check for water leaks as any window can and will leak but this can be fixed with new rubbers and or window sealant. Another source of leaks is from the roof gutters. Because of wet interiors carpets sometimes rot away but can be replaced. The tailgate hinges can rust and stop working and the struts that hold the tailgate open can fail.

Chassis:
The chassis is really strong, but due to their age they can rust badly. Check the chassis front end as rust can occur around the radiator and towards the front end. Also the front suspension mounting brackets can be bad. Check under the car and remove the spare wheel to check underneath. The front chassis outriggers can collect mud and rust away so check under the car and at the rear of the wheel arches. Then check the centre outrigger, which can rust at the top and the end where it meets the sill as can the sills but they are not so easy to spot as they rot at the top. Check the rear suspension mounts as they are important because they hold the rear suspension and the body. They should be rust free and like the front outriggers they also collect mud. Check both under the car and in the wheel arches with the wheel removed. The chassis rear end rust is hard to detect with the body on but get underneath with an inspection lamp and have a good look around the fuel tank. While your there check the tank as the mild steel ones tend to rust through and are expensive to replace. If the seller will let you take out the spare wheel and remove the metal cowling that it sits on and check the front bolted on piece of the chassis that the bumpers and overiders fix to as this can rust away and make the front of the body flex and crack look for cracks above the front wheel arches. You can get replacements easily enough, you can also get stainless steel replacements.  Also check the one at the back that the back bumper fixes too as this also rots but not as badly as the front.

Suspension:
The rear suspension is usually pretty good and not likely to cause problems apart from sagging springs. Check the grease nipple for the bearing has been recently greased.
The front is based on the Triumph TR6. There are double wishbones mounted in rubber bushes. These bushes wear and need to be replaced on a regular basis. The trunnion and the trunnion bolt need regular greasing. If this is neglected the bolt will weld itself in the trunnion and destroy both. There are four grease points on both sides that need regular greasing so make sure they show signs of regular greasing. If there are no signs of grease visible budget for a complete overhaul. The front springs can also sag; distance between wheel arch and ground should be 27" Check the tyres, there should be equal wear and any other could mean worn bushes or worse. A complete overhaul of the suspension is not difficult and reasonably cheap if you do it yourself.

Transmission:
If it is a manual and an overdrive is fitted be sure the overdrive works properly. It should engage and disengage without trouble. Check for signs of clutch slip. Automatics were of 2 types either Borg Warner Type 35 or Ford C3. The C3 is the most common and the better of the 2. All gears should engage easily and check the kickdown works. Check for oil leaks as automatics can leak quite badly but without other problems if they are kept topped up.
The propshafts and back axle only needs regular maintenance and if not neglected are trouble free. The back axle has a small air hole on the right hand rear side. This must be clear as it is the only way to stop pressure building up and forcing the oil out which can lead to premature wear. The differential oil should have been changed on a regular basis but it is common to get a bit of clonking noise from the back axle. This is annoying but nothing to worry about