How do they know the engine has high oil consumption? Because you told them? Sorry I'll have to read the whole thread to find out how many Kms you have done since the last oil top up.
Edit: I don't see any mention of high oil consumption. How often do you need to top it up?
I'm only familiar with leakdown tests on 2-strokes as that is how one checks the crankcase seals. Compression test should be good enough to check piston sealing.
The only reason i can see for a leakdown test on 4-strokes is that some have auto decompression systems to make starting easier, which makes accurate compression tests difficult.