Actually if read Petronas' yearly report, a large part of its revenue is from foreign joint ventures like in Sudan and etc. If I remember correctly, it's more than 50%!!
Petronas' involvement in F1 has given them a lot of credibility internationally and more so when they are competing with the big boys for new oil fields.
And as I mentioned earlier, Petronas would want to sponsor a manufacturer so that they can have benefit with their downstream business as well. It's a win win situation for Petronas.
Latest news,
http://www.themalaysianinsider.com/...o-sponsor-mercedes-gp-was-a-business-decision