I went to the Jiffy Lube this weekend and thought I'd splurge and put
in some Castrol Syntec as they were having a sale on it, (vehicle 2007
Toyota RAV4). When I asked for the Syntec the guy said that once you
go to a synthetic oil, you should stay on it and not go back to
regular oil. Well since the the regular cost of a Syntec oil change
is double, I said forget it and just put in regular oil.

First, is it true what the guy said about it being "bad" to go back to
regular oil after using synthetic? If so, why? I had a car in early
the 90's that loved Mobile 1, ran great on it, I dont remember
dedicating that car to Mobile 1 though for all time, I'm sure I used
all different oils.

Thanks
Rick