I'm going to change the fluid in my Boxster S 6 speed - do it twice?

[Doug427]

My 2002 Boxster S has what I believe to be the original load of gear oil in the trans. It's got 106,000 miles on it and it doesn't shift as smooth as I think it should. I bought the expensive Porsche lubricant for it.

However, before I use that, I was considering running some Mobil 1 synthetic in the gearbox for a thousand miles or so sort of as a flush. I'd drain the old junk out, fill with Mobil 1 then drain that after 1000 miles, to get all remains of the old stuff out with it, then fill with the Porsche fluid. I know that can't hurt things but am I wasting my time and money doing that?