Usually you can get away with just replacing the injector harness, which is about £45 (I think off the top of my head) from a LR dealer...
If you fit this (about an hours work at the most) and then just keep cleaing the ECU end of the plug with brake or electrical cleaner you should be ok... the new injector harness should stop any more oil getting into the engine harness.
If you find it continues you may need a new engine harness - which isn't cheap new - but its not hard to get hold of a late spec second hand one which should stop the problem.
Can supply the bits needed.. or even offer a hand fitting if required
Ian