rokkz, engine oil has nothing to do with anything the flashlube is used for unless its leaking past your valve stems. F0r $70 initially and anywhere from $11 for the Penrite stuff to $18 for the Moreys Lube which is the best, once every 10,000k's once its set right. When i did my manifold gasket, i could clearly see evidence of the flashlube making its way into the chamber. The liquid had formed a coating on the surfaces, not varnish, but almost like vaseline.
Putting in your tank at start up is a waste of time. Use the Moreys System, or Flashlube, doesnt matter, but use the Moreys or Lucas, i not sure about the Flashlube, but the Moreys has a higher flashpoint and does not burn like what the others do and layers the surfaces and moistens the charge entering the chamber. Drill a whole on the top of your plenum behind the throttle body, insert a brass fitting and stick your hose on it. This way it distributes evenly.
No one does anything, installers will tell you you dont need it cause it makes them look like di&ks for not including it, but they all stock em on their shelves (Just like stainless steel leads that they never install for you, unless you ask or they use it as a fix once your car starts backfiring). Ask a few head specialist and ask them if you need one. Yes tune is probably the most important aspect, best to run it slightly richer, than lean to get extra mileage when you already saving over petrol anyway. With the moreys with its higher flashpoint, it coats the upper cylinder in the hope that it will help seal as well, but you could never really guage this.
And definately do not use a 10W-30 oil on a LPG car. The lightest you would wanna go is a 15W-40 SL or SM oil with a Diesel rating(CF/CI) to cater for the extra acids in the oil. Even use diesel oil, Mobil make one of the best. LPG burns so much hotter, it would thin the 10W-30 to water(remember coolant only takes a percentage of heat, oil has to cool the engine as well) , you shouldnt even use 10W-30 on Petrol car. Holden sell a 15W-40 LPG oil, it may be rebagged Mobil or Fuchs oil. You dont need the specific LPG oil, as long as the oil has the C rating as well as a SL/SM rating, you can use any oil. I'm not gonna go on about brands, theres heaps of threads on the net. On lpg you will see the oil only ever darkens at 4-5000k's as it doesn't suffer from fuel dilution as much as petrol cars, but does build up acid. Good spec oil and easily go to 10,000, although some brands are only made to last 5000k's.