That's getting on a bit now, but at the time it was probably the highest quality light lorry you could buy, over engineered as only an MB can, a company director i know well had no end of trouble with other makes at the time, i pointed him at 814's and they ended up with a small fleet of them which gave sterling service for many years.

If it's been looked after well (but does anyone look after horse boxes properly?) then it should go on for years if the tin worm hasn't got to it.

I certainly wouldn't dismiss it purely because it's a non tilt, if it was designed properly as such then the engine access can be surprisingly good from under the seats, the only real issue is if the engine has to come out which is unlikely, most servicing is straightforward, often more pleasant if done outside in the weather cos you're under cover anyway..:-)

I'd pay a lorry mechanic to check it over if it were me.