Mitsubishi Part # MC840219
BWD Part # S4010
Beck& Arnley Part # 2010445
You can also source them from local tractor/forklift places.
North american cross reference application : ECP0056 MITSUBISHI 6D14 SENSOR
The stock sensor is not a complicated piece of engineering that is proprietary to Mitsubishi. Any of the above sensors will suffice.
The oil sensor is used in other vehicles and with other brands as per above or as .:FoRuM56:. mentioned, over in the UK at Milner's.
http://www.milneroffroad.com/index.php? ... uct_id=560
I order mine through wakefield sperling or lordco when needed. This is not a case of 'OEM' part mandatory. In fact, the beck&arnley one is still going solid for 5 years in the L300 and I've gone through three OEM Mitsu's on the Pajero.
Order which ever you prefer. There are always options out there.