Expansion tank hole

[WhyTwo]

I think my expansion tank has 'blown a hole' but I could be mistaken.

Should there be a small hole where the arrow is pointing in the picture below? It's on the underside below the seam, probably about 5mm. If so, what should be plugged into it? I can't see any tubes that could be plugged into it.

I've ordered a new tank but it's bugging me how it could've developed this hole. Coincidentally it was sat at 4k revs for 3 mins on the MoT emissions test getting super hot just before this problem surfaced

[N1CERB]

Its a pressurised tank so should not have a hole in it. Probably just over pressured and found the weakest spot and blew a hole in it.

[Boatbuoy]

That's on the seam of the two halves of the tool that moulded the tank and is therefore the weak point, as mentioned above.

[WhyTwo]

As I suspected, thanks fellas. Replacement ordered from Europarts as per the alternative parts list