Hell what a question, now you've done it, opened a hornets nest, there are 5,000 recommendations on here about what is the gun oil for TD42's, everybody has their own opinion that the oil they use is the best.
I've had a couple of GQ,s with mileage getting up there and a bit more, I used to use Penzoil exclusively for many years because it was the only oil that had a demonstrated fuel saving benefit, till Shell took it over and changed the formula, it went to chit.
I changed to anything that fit the budget at the time, with no detriment to the engines, I have tried everything except the ridiculously expensive oils over the years and never noticed any difference, they all turned a very deep shade of Black after about 5 minutes running time.
My current preference is Shell Rimula 4 X, but that is on a brand new build engine, any middle priced name brand oil will be OK. Don't get sucked into the Jasco/ Nissan oil hype rambled on about in so many threads, these old clunker engines don't care just so long as it is slippery.
You will soon formulate your own opinions as to what you think makes it spin better, run quieter. One thing I would suggest you try is after your oil and filter change run a 1/2 tank of fuel through and take particular notice of engine noise, then put 250 mils of TCW3 outboard two stroke oil in the tank and top off the tank and go for a run for about 20 mins and see if the engine runs quieter, I bet it is.
the first time a put 2 stroke in the tank I thought it was quieter but thought it might have been a placedo effect and I was fooling myself. Never said anything to the missus and we went down the local supermarket and after about a kilometre she asked what I had done to the engine, I said why, and she said it is a lot quieter and smoother than it used to be. So even She Who Must be Obeyed noticed the difference, and she has the mechanical ability and knowledge of a mosquito......
The reason being the fuel pump and fuel injectors are being lubricated better, and the fuel burn changes a little because of the oil, so is definitely beneficial, also helps fuel economy a bit if you do any towing. The oil is totally soluble in fuel and will do absolutely no harm, it is formulated to be burnt mixed in fuel. Gulf Western TCW3 from Supercheap is the go, also cheapest, no real benefit from burning more expensive oil.
Sorry to get off the engine oil topic, but being a newbie thought I would bring it to your attention. there are long threads on here about 2 stroke oil in diesel and what is the best engine oil, and reading through them all will take a month and do your head in.
Cheers and good luck with your patrol, hope you have many happy years motoring in the old beastie....