Hi was going to change gearbox oil in my 2009 6 speed 120 hp 2.3 ducato.No issuses just fo the sake of it.Went to dorset auto gave all details ..they supplied this..a mineral oil..where book says synthetic base...so not changing until i know what's what..please advise,I know it has to be GL-4..this also says GL-4+ ?..please advise.