Hey FC( ya know you can get arrested for that in some states
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I'm not familiar with the aircraft in question, but if it's a type which has framing, perhaps you can cut the cracked section out & substitute some acetate or lexan? Maybe show it open so as not to make it obvious? i tried this with a Bf109 a long time ago, & someone with talent could probably actually make it work
Other than that, I'm afraid you may have to replace it. If the kit is still in production, companies are usually pretty good about letting you order replacement parts. Of course, if there's a possibility it cracked in shipping, some companies will replace it free.
Other options are Aftermarket(Merlin or Holdfast can probably steer you that direction) or vacuforming a replacement using your original as a guide.
HTH!
Oh, & Welcome to the Site!
[EDIT1]- D'oh! The Merlin Helicopter!( sorry, been at work for over 12 hrs now...)Hmm. If it's one of the side windows you can cut it out, but if it's the front Wraparound-'fraid your like a duck at a Cockfight...
[EDIT2] - I see you've been a member since October...well, welcome BACK to the site...