There is nothing wrong w/ M1, many of us use it w/o issue and have done so for decades, have they changed the formula in that time, yes, but it is still a fine oil
Mobil oil info
there are many different lines of Mobil oil, I use the 15w/50 listed second from the bottom on pg1 above, there are some that prefer the V-Twin 20w/50 listed 3rd from the bottom on pg2 because it has more ZDDP, it is a lot more expensive and the additional ZDDP is not necessary. Avoid the 0w/50 listed last it is a racing oil and will need to be changed very frequently, Avoid any ACEA A1/B1-08 rated oil
Porsche recommends M1 5w/50 listed 4 from the bottom for all Porsches ever made, but I'll stick w/ 15w/50
Nothing wrong w/ Brad Penn or any of the other boutique oils except cost and availability