Sticking valves fix??

[rockyrivermark]

So I got s small block that has been sitting for several years.
Seems like valves are sticking. Thinking intake bit maybe an exhaust or two also, not sure.
So I've heard pouring marvel mystery oil down carb , in gas tank and also adding it to the oil. Seafoam help?
I was going to take valve covers off and spray some penetrating oil around the valve stems. And add mystery to the oil.
Any suggestions or info greatly appreciated.
low mileage engine.
Thanks
Mark