When I was at Oshkosh the US rep was turning the business over to someone else and going into semi-retirement. Matt was the main guy for 30 years and has a wealth of knowledge. He still provides technical support for the new group. When he was in charge, he had a friend that worked in an Oil lab and he had a blind test done with many different 2 stroke oils. BlueMax came back as the best and what he recommends to use for Hirth engines. Anyone with 30 years of knowledge with a certain engine get my vote of confidence. You can order the oil from him, below are the details.
Recreational Power Engineering - Hirth Engines - Tiffin, Ohio - Factory Authorized US Distributor (recpower.com)
RPE@bpsom.com = email, ph 419.585.7002
3+ gallon orders are the cheapest and they come in 32oz bottles.
The mix is 8oz per 5 gallons of fuel.