The fluid in my 2005 Larson, with a 4.3 190HP SX is low, I've read that I can use any automatic transmission fluid in it. Is that correct? Thanks in advance.
I can say that Dexron III works fine in Johnson/Evinrude outboards. Other engines I have no experience with, so unless someone else chimes in who has experience with your type of engine/outdrive your best bet is to post your question to the appropriate engine repair forum.
Add more of whatever is already in there. Mixing fluid types is not recommended.
It is a bad idea to add ATF if the system is already half full of 30W Oil.
There should be a label on the tank or stamping on the cap saying what yours uses.