One sentence sums up this van - can't kill it. Our first one did 550,000kms, our second is on 330,000kms and we had two Vianos that did 400,000kms (airport transfers). The ultimate in turn the key and go commercial vehicles, the Vito's underpinnings are the same as it commercial van brethren and it is as tough as nails.
Not without faults however...the Vito doesn't have the more expensive and better equipped Vianos self-levelling air suspension, so the ride can be harsh, especially with people on board. It doesn't have the Vianos sound deadening either so the agricultural 4cyl diesel can be a bit tractor like in NVH levels. The Vito has the commercial vans heavier steering as opposed to the Vianos variable assistance effort and the dual air con while very effective, sounds like a 747 taking off.
These are big heavy vans but surprisingly maneuverable and they go stop and steer very well. Brakes in commercial use will last maybe 30,000 km and the rotors will need replacing - side effect of good brakes. The legendary MB brake soot can be frustrating but a good wheel cleaner such as Bowdens 'Wheely Clean' is worth it's weight in gold.
Even when neglected and underserviced you can still jump in one and do a long trip - they are tough old girls. Some have a quirk where the LHF tyre will wear quicker but there is an internet fix for this, as is the removal of the front fan blower motor which MB tells you to remove the dash - erm, no. Watch the bulbs and buy top quality Phillips ones which last the longest.
Take it from someone who depends on these vans for income - never ever skimp on oil quality the engine will repay you in high mileage. We used Mobil 1 or the Fuchs synthetic equivalent (MB use Fuchs now instead of Mobil) and replaced oil and filter every 15,000kms. Auto transmission service every 30,000kms and if you do it yourself pull the battery for 30mins and let the trans programme itself with fresh oil (Benz tell you trans service every 60km but if you work it hard, halve that). Brakes are easy enough to do yourself and like all Euro can parts are dirt cheap on fleabay. Watch the shocks they can leak or go soft quick in hard-working vehicles but cheap online.
The coolant overflow and windscreen washer bottles may go brittle from age and the air con condenser and radiator like a blast from the jet washer in the car wash every week. Watch all the fluid levels religiously and carry top up litre bottles in older high mileage vans.
That's it - highly recommended, great on fuel, tough as nails and that badge on the front goes down well with customers. Pulls a trailer like it's not there and does that with 8 passengers easily day in day out. Look after it and it will be a loyal hardworking asset for many years in the future.