I've had the same problem with other plastic to PE attachments. I cleaned both surfaces up with mild soapy water and a good rinse then made sure the was a good flat surface on both parts for a very very patient adhesion. I hope this helps.
On that note I guess it is time to start my own Butcher Bird project:
The Kit: 1/32 Hasegawa FW 190 A-8 JGr. 10 "Red 8"
http://i1279.photobucket.com/albums/y523/rich750us/IMG_1819_zps788e954e.jpg
The Aftermarket Upgrades:
http://i1279.photobucket.com/albums/y523/rich750us/IMG_1820_zps82a46f78.jpg
The References:
http://i1279.photobucket.com/albums/y523/rich750us/IMG_1821_zpsd77d7c5e.jpg