As long as servicing was carried out at proper intervals, there should be no
concerns with the base stocks that the oils are built on. If you prefer to
continue running conventional motor oil, do do... Even in my harsh winter
climate, I find it hard to justify the extra expense of synthetic motor oils
(though I do run synthetic in my drive axles).... also remember that all
synthetics are not created equal (Google "polyalfaolephin").

Even though some producers are touting their oil as "extended change
interval capable", I am somewhat leery..... my view is that it is the oils
"add-pack" that deteriorates over the life of the oil and not the base oil
itself. As foaming is prevented, the antifoamants are consumed or altered,
as oxidation is prevented, the oxidation inhibitors are consumed and so on.

If you know the previous owner, both of you would have been further ahead to
swing a private deal and keep the dealer from getting his pound of flesh out
of the transaction...

Just put Mobil 1 back in when you change the oil. No big deal.
    Jack   
Giving up the right to arms is a mistake a free people get to make only
once. I will not make that mistake.