Risk lies with the owner. I did see that the dna expedition filter I have for my gs did get fine dust with an offroad riding trip I did. I now use the oem paper for all off road rides.
This air filter test dealt with dirt and flow and included a K& N filter. Flow is one thing but dirt ingress especially off road suggests OEM use only for gravel riding. There are other tests on the web basically saying the same thing.
https://www.project200.com.au/dm-iso5011/
If you have a local Outdoor Warehouse handy - the elastic they sell in 5m lengths. I needed some for one of my tents 2 weeks ago and found it at my local O W outlet. Easy to redo.
When I was playing with power commanders on sports bikes I used to run the fueling map at low throttle openings in economy positions and any throttle opening larger than 15% was at full power afr values. I would expect that electronic ignition curves could be manipulated to achieve a similar...
The problem with any vintage or classic here in South Africa is that the cost to restore or even just get the required parts from elsewhere in the world is prohibitive. I used to do british bike restorations as a hobby but its just too expensive now.
The revving is really weird behaviour. I was riding my gs behind a fellow on a sports bike down hospital bend a while ago and he was revving all the way despite tge dact that the space before the rev was wider than I needed. Stupidity has no equal.
It must be nice to have a clean diesel engine. My X5 has oil and filter changed every 5k km with shell ultra. Oil is filthy after 5k. Perhaps it's mostly town driving? The egr has been blanked off as I thought that may contribute but it hasn't made a difference.