Haros

I'm looking to buy a first generation x1 xDrive. I know diesels give better mileage but I'm asking purely in terms of reliability as I've heard the timing chain is prone to stretching on the diesels. Is this is a common issue? Also, does the diesel have problems with fuel getting into the engine oil when the DPF is regenerating? I know a lot of diesels in general have this issue regardless of make/model. Any additional advice between petrol and diesel models would be greatly appreciated.