It's extremely hard to say what the cost of a rebuild will be and at what point rebuilding sooner rather than later would save money. If a pre-chamber insert breaks in half and falls into the cylinder, it obviously would have saved money to rebuild it the day before... In a similar way, you might get another 10 years of driving out of a well-running engine and your life situation might change causing you to decide to sell it in 3 years... In that case, the cost rebuilding vs. not rebuilding would be a darn sight more. Usually people rebuild when the engine has an 'issue' because that's usually the time when they need to. I can't really give you better than that.
The van goes really well, engine is great as is... the only weird thing is when going slowly over bumps the steering wheel seems to shake a bit like it is loose! ...I am guessing something is loose and getting warnout in there.The other thing is the brakes squeek a bit when going slow and braking... he said the pads are still quite good but need replacing pretty soon - so maybe they need replacing NOW!? Better have a look ASAP!
...the guy I just bought it off HAD a 1.9 TD in there, and he very much preferred it!