Cracked deck plate

Some friends of mine are about to pull the trigger on an IP 420. Apparently, it has a cracked (broken) deck plate.  The owner claims it was replaced with a 2 piece deck plate.  That sounds sketchy to me for a number of reasons.  Has anyone heard of such a thing?  Also, what reasons other than sever trauma would cause the cast aluminum plate to crack in the first place?

My friends are in the UK so they aren't able to view it in person.  Below is a picture they received:

   

Thanks!
Carl

Check out Isomat deck plates at Rigrite. Isomat spars are common with island packets, may be true also for the 420 as it sure looks like it. There are no two part deck plates o have seen but it is possible that it has a specified mast wedge collar that fits with it. Cast aluminum is very brittle and can crack as cast iron. Seeing the crack is by the screw, it could of been overtighted or stessed if the plate was not uniformly flat bedded on the cabin top. It is replaceable but will require mast un-stepping.

Adding to what Aquavit362 said. I have not seen a two-part deck plate here before. Yes, to install a new single-piece one requires pulling the mast.
Damage assessment could show as simple as Aquavit362 said. However, I would carefully inspect the mast partners where they enter the cabin top AND the keel mount plate to determine if another more serious trauma occurred and if that caused damage downstream.
Mac McDermid IP37 "Hamba Kahle"