DON'T use soudal fix all or another adhesive/sealant!!!! .First off the crack needs to be stopped , a crack is a like a lever, the two sides of the crack(lever) exerting enormous pressure on the end of the crack (fulcrum) and even with a good adhesive/sealant the crack will continue to grow over time. First off drill a small ( 1-2mm) at the end of the crack to stop it progressing. (this is a tried and tested engineering procedure) , then use an Acrylic solvent adhesive like tensol 12 . The kits usually come with a syringe and a micro applicator. There are other suitable low viscosity Acrylic adhesives , Locktite do a version of superglue which is specific for plastics, again its low viscosity allow the adhesive to seep into the crack ( using capillary action), whereas Soudal Fix all or Sikalfex are medium to high viscosity and won't penetrate the crack. There is a company called EECO based in Halifax who will refurbish windows , I have just referred a client who had a delaminating window and he took the window to them and they refurbished it there and then for reasonable money.