I saw this and thought it was a good primer on using the myriad of sealants and RTV's out there. The only caution I would add (to reinforce the caution in the paragraph on Shellacs) is that Shellac sealers work really well, but you almost have to use dynamite to get things apart once they've been sealed with Shellac and, as they say, it is a real bear to remove the stuff and its residue.
Here you go: Sealants 101