Hi,
Had a 91 Kontiki 640 /6 Talbot 2.5 Turbo Diesel for Three years as our first motorhome with 70K miles on the clock. This was the Rear lounge model which seemed to be the preferred layout.
I found it Ok to drive, however my other half would not drive it as she found it too heavy without the power steering. (would recommend this)
The only work needing done to the van during that time, other than routine Maint. & a couple of new tyres was a clutch change.
When fully laden for a 2 x week tour with the family It did struggle a bit on the hills, however it was just a case of getting used to working the gears.
Overall I found that for its age, the Kontiki had all the gear / specification you need for family touring, in all seasons, coupled with plenty of lounging space, and returned around 25mpg.
A good condition Kontiki will also hold its value well against other vans of a similar age.
Best of luck with your search,
Cheers,