Hi Mr. Bill,
Thanks for your sage advice. Just to clarify, the under-hood "smoke" is clearly diesel exhaust. The engine is quiet at both idle and under load (hot and cold), so I don't think it's a cracked exhaust manifold. If it were a gas engine, I'd say it's more like an egr issue.
Re: the PPI, the car is so cheap as to be almost free, so I can take the risk on a rust-free chassis, clean interior, tight running gear, new rubber etc. The known problems are vacuum issues... central locking and engine cut-off. I'm going to give it a cold start tomorrow and if it handles that well, I'll probably buy it. BTW, I had a Volvo (VW) 6 cyl td previously and this MB sounds much better than the Volvo ever did.
Thanks for your insights.
Mr. Wheelman

'88 Volvo 745 255,000 mi.
'90 Volvo 744T 176,000 mi.
MB coming soon....