I am also looking for a M35 at the moment, the main things that i will be checking for are:
Inside of wheels for wetness, as this could mean the axle seals are leaking or even worse brake cylinders.
Master cylinder fluid level. Please be aware these trucks have a single circuit braking system a small leek could lead to no
brakes
Tyres, for cracking and wear.
Check all other fluids, oil water, when checking oil make sure it doesn't look to thin and smell of fuel, these trucks sometimes leak fuel into the sump through the fuel density compensator.
Engine running for leaks especially around head gasket area and turbo charger.
General condition of vehicle e.g. bodywork, lights, glass, canvas an so on.
Good look with your search