Best oil for Merc 4stroke?

[Mudslide]

I have a 2005 90 HP Merc that I want to do an oil change on The Merc oil seems to be way way overpriced. Can I use a good quality synthetic or should I bite the bullet and run the Merc stuff. Is there really a difference?

 

[vetteman]

What specialty produced oil(Marine/ATV/Motorcycle) isn't overpriced.Sometimes you pay more than you do for a good synthetic oil.As long as you use the weight and performance grade Merc reccomends you'll be fine.I use Pennzoil in my 8HP Merc and in my 20 HP Yamaha.
Dave

 

[Cedarstrip]

I've got a 2002 90 Merc. It says to just use plain old 10w30.

 

[doger5]

I run Amsoil 10/30 marine .
These are not car engines thay have great loads and work hard ,if you want to keep it for a long time take care. ( Oil Cheap )

 

[Mudslide]

Note: AMSOIL Formula 4-Stroke® Marine Synthetic 10W-40 is recommended for use in place of 25W-40 as specified by Mercury®.

http://www.syntheticwarehouse.com/outboard_synthetic_oil_10W40.htm

Mercury seems to call for 25w-40 for warmer operating temps and allows for 10w-30 for very low operating temps.

I guess my question wad: are the marine specific additives which are mostly for preventing corrosion needed if you use something like mobile-one full synthetic?