Robert, The sega may be corroded/damaged too much, possibly good for some parts, but if you would like to give it a try, I will post a couple links that may help.
Use the 1st link below to see how to tear down the Sega genesis, after tear down you will be able to see other damage and if incline to continue, clean board and all connections being careful not to dislodge components,etc. 2nd link some instruction on cleaning electronics that have gotten wet. Good luck.
[guide|3770]
[[Electronics Water Damage]]