I`d say with "good seals" no leak ,no problem ,but with "leaky seals" it may leak quicker....
got Mobil 1 synth in both my daily driver and the bird....
yes the bird has a slight leak around rear main ,but not any more pronounced than with 'regular oil'...I actually tried a thicker oil (thicker regular oil than my 'normal ' regular ) for a short period to see if I`d stop the leak, but all that happened was I ran very high oil pressure, didnt dare to keep it that thick, never had time to check for the leak, since it scared the c*ap out of me reading the pressure gauge...! :rolleyes: