I own a 1984 300GD which is a little smokey at idle especially when cold. The motor has done 260,000 km (162,000miles) so it may just be getting tired but I'm thinking it could be leaking oil through the valves.
How difficult is it to replace valve guide seals on this motor?
Are the parts expensive?
Whilst doing this job, is there anything in particular I need to pay attention to?