I Must Be Doing Something Wrong

Sounds like they might be old,have you had the kit for many years ? If you have other older kits,you can coat the decal sheet with this stuff http://www.microscale.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=MI-12&Category_Code=FINPROD&Product_Count=6  it might save them.

unfortunatly the only thing to do with the damaged ones is to get after market decals for them.

I second Tojo's advice.   That product is inexpensive and  cures a lot of ills,  however if they are ancient decals it still may not work.  Hopefully you can get aftermarket for the particular subject and scale.

Every modeler should have the Microscale decal solution on hand.

Many decal sheets have all the writing and designs made with the decal film over them, even the company logo and writing identifying the particular sheet. These little images are not used on the model.  If a kit is old and I suspect possible decal problems, I will test the sheet by trying to apply one of those extra decals to a piece of scrap.  That way I will know if I need to apply decal film before I lose any of the decals necessary for the model.

I also now always scan decal sheets, so in the worst case, If I screw up any decals I might be able to make inkjet replacements.

Django

The last model (Hesagaw FW290 : 1/72) was ok until I tried to apply the decals. No matter what I did, they dissolved or tore apart in my hands. I don't recall that problem years ago. What a mess. Any tips?

I've had the same problem with two Hasegawa kits recently, both older releases. Soaked them in HOT water with a drop of dish detergent and was able to use 95% of them.