A reported heavy engine oil usage (almost a litre/100 miles) with no apparent burning of oil or excessive smoke from the exhaust could be the result of the following – common to the Mercedes T1N earlier Sprinter models.
It is worth visually checking the oil supply banjo bolt and washers on the top of the turbo unit, unless you are very unlucky this steel pipe and its unions will be all tight and dry of any leaks.
High rate oil loss may be the result of the sealing washer on the turbo oil return to sump pipe being worn/split and leaking (Item number 10 in the diagram below). The fact that you may have noticed large amounts of oil around the engine on the turbo/resonator side could be indicative of this problem.
If you follow the half inch steel pipe that dog legs from the underside of the turbo to the seam between the block and sump pan, this point of entry is the place to look. Clean it off and have a peek, even at idle poor sealing here will be indicated with a very visible oil leak. The seal itself is like a rubber top-hat that wears due to engine vibration. I have even seen the return pipe wall material wear through to the point of leaking as it passes through this seal.
Lubricating oil passing through the turbo circulates at a ‘gallons a minute’ rate and trouble here will cause some rapid oil loss.
Either way it would be good to jet wash the engine off, so you have a better chance of locating any leak and a far more pleasant environment in which to work when rectifying the problem.
If you do find this to be the problem, replacement is quickest done by taking off the complete exhaust manifold/turbo as the return pipe is next to impossible to remove in situ.
If the leak persists, then you need to wipe off the return pipe and look underneath with engine running. If there is oil travelling down the outside of the pipe from the turbo casting, chances are the top hat seal flange section of the pipe as fractured around the radius. This is a fault I have seen a couple of times. No amount of gasket, compound or tightening will ever stem the flow, there is likely a crack as the pipe is flanged out and the only way to detect it is to take it off, plug the end and blow!
Obviously if the leak is internal and the turbo hoses are full of oil then you have a different problem…
I have stellar mile sprinters on my books here that really have some pretty big blow-by crank case pressures from worn piston rings / bores. These breathe quite heavily through the oil separator on the rocker cover but do not consume a great deal of oil in daily use.
Another place to take a look would be the oil filler cap! I have had a couple of these that have split /cracked on their edges. The oil filler cap is wonderfully positioned to take the full force of oil fling from the timing chain under any running conditions, oil obviously works its way out through any failings here. It will usually run down and back – sometimes giving the impression the separator is leaking. It is not uncommon for it to run down and soak the alternator and any dripping from this base of the generator/alternator is always worth tracing to what lies directly above.
It is also worth noting that oil will distribute itself on a running engine in what can be sometimes very misleading ways, being blown about by the cooling fan and the action of the vehicle in motion. In any event the best way to proceed in a situation where oil is leaking and you are unsure where from, is to clean off the engine with Gunk or other degreaser and watch and wait with an idling engine. It is sometimes useful to place a piece of hardboard beneath so drips can be easily located and hopefully traced.