Leaking Windows

[Raw Slaw]

After pulling, scraping, cleaning, and caulking our windows, we still have a bunch of leaks. We used silicone weatherproof window caulk, put insulation board pieces in the big gap at the top of the window, and then used Great Stuff foam to fill the gaps from the outside.
So, what should we do now? We have to pull them out and reseal, but I'm terrified of having to do this a third time if this next shot doesn't work. I've heard people say butyl tape. Do you just put that around the edges like you would caulk? Is this sufficient or would I need an additional caulk like elastomeric sealant? Thanks.

Links to products appreciated. Really bummed we blew this money only to have to pull them back out.

[slaughridge85]

That great stuff foam is an open cell foam product. If you want it to be water proof you need to use a closed cell foam...

[BusFiend]

Many also recommend butyl caulk over silicone. Auto manufacturers use butyl for a reason, I suppose.

[jazty]

For a good seal on metal I would recommend one of the thermoplastic caulks, or butyl tape if you can properly sandwich it between the flanges. Never much cared for that silicone stuff..

EDIT: Supra expert is my favourite thermoplastic caulking so far. No affiliation, not trying to sell it, it's just my go-to for sealing steel stuff. It doesn't crack like silicone does when stretched.