UKC

I was thinking of rebolting this, just the belay, as it's hangers are pretty corroded and the chain is rusted and not equalised. Also the bolts are expansion bolts which would be more prone to seepage, which in the wet cave means they are more likely to have hidden rust. 

Was thinking of putting in a glue in with 316 stainless anchor. 

Anyone got a problem with this ? Lol

No one would object to you replacing an old belay but here are a few points to consider.

It is not necessary to equalise the bolts in a chain belay. It is more important that the bolts are located it solid rock a safe distance from one another. If you have previous experience with resin bolts then they are obviously best but a cave is not the place to learn. 316 aka A4 expansion bolts would work perfectly well too. No point over engineering the belay if the rest of the bolts are in a poor state. The belay doesn't take falls.

Personally if I was going to do it I think I would replace the chain with a discreet threadable twin bolt as the cave is a popular beauty spot, a geological wonder.

Cheers mate. I place resin anchors at work regularly.

Twin glue in  threadables seems like a good option.

I second not using a chain, I went before I was a climber and had no idea what the chain was for and thought it was ridiculous being there