Is there a standard oil weight for new forks out of the box??? When I change mine out can I change the oil weight??? How will going with a lower weight or higher weight affect the performance???
What he said. It depends on the manufacturer. Marzocchi uses pretty much the same oil in everything: a 7.5 wt oil.
Rock Shox oil varies depending on the whether it's on the compression side or rebound side.
I don't know what Manitou or fox does.
Be warned about using fork oil from a moto shop. Most moto fork oils contain seal swellers... you don't want that in bike forks. One really good moto oil is Golden Spectro (what's actually in the Marzocchi oil bottle), but very few shops carry it.
BTI-usa lists a number of oils in their catalog that most LBS's can order.