BlueTac can sometimes react with paint & leave residues, so I use White-Tac instead, slightly less tacky, & hasn't yet gone icky..
Try rolling a fresh new lump bluetac over it, as I think soapy water tends not to work?, therafter something lite like Medea airbrush thinner, provided it doesn't marr your paint.
Silly Putty is hard to find in the UK, & Panzer putty is too expensive for what it is for my cheap-skate mode...