identifing what exactly is leaking would be the best start - soapy water will allow you to locate it, or alternatively a gas leak detector spray, if its the hose connection then if its as tight as it will go you might want to renew the 12mm hose rather than risking breaking the pressure sensor as the old hose may be too hard to shape properly round the sensor.
It may not be the injectors that were leaking - if your vapouriser has a vacuum line it may be worth checking that its not leaking gas through that way into the inlet, either put the open end of the vacuum line into some water when its running and check for bubbles (the other end should still be on the vapouriser) or check if you have any pressure coming out of the nipple on the vapouriser (while the engine is running in both cases)
Hi Brian, the current leak is from the new T piece I've just fitted. The 12mm hose is all new too. It's leaking from the 'take off' grub screw in the T piece. I shall try sealing it with some plumbing sealer I have.
As for the original problem, it was far too random to be leaking from the reducer. If it was, then surely it would happen all the time?
My guess is that just one injector was leaking, and if the engine happened to stop with the inlet valves of the cylinder in a particular position, it would allow the gas to enter the plenum and be ignited by a 'wasted spark' upon starting the engine. This would certainly explain the randomness of the occurrence.
I've now changed both injector rails and time will tell if it's cured the problem
Can't suggest much else on the leak - you know where it is at least. With the injectors it depends, not so much on the position of the engine, but if it is leaking it will fill the manifold/plenum up with gas, this might dissipate with time, also the amount of gas would depend on the pressure present when you stopped the engine etc.
Easy way to tell if its happening is to look at the pressure reading in the software if you have access to it - if when its not running on gas it stays reasonably stable then you should be ok leak wise, if you can see it gradually dropping its still leaking somewhere between the vapouriser solenoid and the injectors.
Fairly random would expect to be injectors though, and given they are the age they are and fairly cheap to purchase probably best to swap those and see what happens as you have done.