Envirotex Lite is a liquid 2 part mix and pour. Its used for bars and table tops to seal photos and stuff. I've gotten it at Ace Hardware stores.
I had the exact same problem leaking under the spring seats on my original 255hp 441 heads and this stuff cured the problem for good.
position the cylinder head upside down so the leaks are the low poins........... mix the stuff up in coffee can and pour it in. It has the consistency of cold pankake syrup. Roll the head around a little to help with the flow and then set it down upside down again over night. It will settle in all the spring pockets.
There might be better stuff out there now... but if your stuck....... my experience with this stuff was good and its easy to get. If you have any left over you can make a nice plaque with it. LOL.
click on the link to read about it
http://www.eti-usa.com/consum/envtex/envlite.htm