The track day was way back after my 1st or 2nd sample, Blackstone simply keep forgetting to remove that! And i always warm the engine up sufficiently and wait for a couple of litres to flow out before getting my sample.
The latest sample of oil (the one in the link) was only after about 500 miles or so on LPG, so cant really comment on it. But trends have been set, and so i look forward to seeing what the last 8000 miles on LPG will show, will be sending the sample off this weekend.
LPG burns more cleanly and i did notice the oil drained looked cleaner to the naked eye, but still not as clear as i was expecting, or have seen on my cousins 1996 E36 318is (still running strong at 170K miles!! LPG'd at 60K), his oil comes out very clear, although he does use an engine oil cleaner (wynns) just prior to an oil change (similar to seafoam).
However from my reading LPG does create higher engine temp spikes, leading to possible premature valve (seat?) wear, but this doesnt seem to affect BMWs, Audis, and Mercs much at all, with converted engines in general lasting longer. Also i understand that because the LPG is in a gaseous form in the cylinder it doesnt "wash off" the inevitable but benefical thin layer of oil that coats the cylinder walls, which is especially important when you switch off and then restart from cold as some of that layer of oil ought to still be present.
For those who arent familiar with LPG systems, they still have to start up on petrol, and auto switch over at about 40 deg C coolant temp. If the system senses that the engine will be starved of LPG for whatever reason it will automatically switch over to petrol and alert you to this. Petrol in the UK costs £ 1.20, and LPG costs £ 0.59 (basically half). But of course lower calorific content means mpg drops by about 20-25%.
I'll post the latest results when i get them.