Hi..there apologies for the delay..
If the injectors are indeed leaking fuel/gases blowing by them..then unfortunatly is not as straight forward job as some think..as the injectors can get siezed,pretty badly in the cylinder head..this in turn requires a hydraulic puller to with draw the defective injector(s) from the cylinder head..specialist companies normally have these specific pullers to carry out jobs like this if slide hammers dont work.or manual pullers fail to get them out....If its worth doing? Thats really upto you im afraid,whether its financially viable? you would need to get certain quotes ideally on the injectors/code/extracting and refitting- depending on the rest of vans condition and age and of course to the mileage if quite high - might not be worth it to be honest...
Depends how bad they are or one of the injectors is or that mentioned leak..as injectors dont leak oil they would leak fuel so if that leak smells of diesel or all around the injector body is soaking wet or black/fuel smelling sludge then you know that the source of the problem as per injectors or one of them..if an oil leak then that would need to be further investigated id say.and obviously as far as injectors goes you would only know that if they where removed and tested.it might be overfuelling or loosing pressure which would cause starting issues either way would cause problems down the line at some stage...if it isnt actually effecting performance/or starting etc..then it dont see why not using for as long as you can..you could of course try one of these injector cleaner addtives into the tank of fuel and see if that helps,buy time so to speak...but the problem will have to be addressed at some stage