'98 5.2 A/C problems

A/C does not work in my truck. Compressor, clutch. etc fine, function normally. Recharged refrigerant two years ago, held charge all summer. Recharged last year and it lost it after a week. Have run dye, unable to locate and am unable to do UV leak tests.

Just wondering if any of you have had this problem (similar year, engine, etc) and if you have tried these "A/C system sealents", here is a link to one of them:

http://cliplight.com/automotive/products.php?pageID=Product_Details&productID=16&catID=4

and a link comparing Super Seal to other quick fixers:

http://cliplight.com/downloads/946KITPremiumComparison.pdf (PDF)

Would any of you recommend against using these (other than those containing hc) for any reason?