5W is more like a Winter oil, most of the dealers I know usually use 15w50 and for some older big V's 20w50. My last service on my MV was done with a 10w40 which I changed after as the lady was burning oil during summer.
it did not lose it, it burned more oil than usual. I am not a casual rider which goes on trips every weekend, so my riding is going back and from work plus some detours if time permits. A month is around 2500km so with the 10w40 she was burning 1/4 liter during July, after I changed tall my bikes to a 15w/50 except the 2 Ducs and the consumption dropped to 150ml for the following 3 months.You mean, running on 10w-40 your bike lost some oil ?