I have used Millers VSPe in all my older, non-cat, classics ( Minor/gazelle/minis/Rover p6/MGB ) for the best part of 10 years and before that when it was VSP, have never had an issue - its good stuff and worth checking out.

https://www.halfords.com/motoring/e...pe-powerplus-multishot-500ml-130850.html

Available from amazon/ebay etc etc.

2015 Morgan 4/4 (Wolf fettled) previously 2014 M3W
MINI Cooper S and numerous BMC/BL relics.