Halfrauds do a top up system, a gun with a gauge and a replaceable tank of gas that includes the right amount of oil and a sealant for small leaks. I've used this on two Discos, never had a problem and it seems to do the job. Obviously with a leak that becomes apparent again within two weeks then you'll need to shell out for a garage to find it and cure it. The trick apparently is to follow the instructions to the letter but then when filling to hold the tank upside down to maximise the leak sealant, as it tends to settle in storage.