Our Unused Front Door

I've been looking at our front door, which we haven't used as such since we moved here in 2009. It's much less convenient than the door in the kitchen, and it's a bit fragile.

I don't want to replace it, as that would be costly, and it doesn't need to be fully insulated as it only leads into a porch which is fully insulated and has double glazed doors. It's also very large - and original. I'd like to re-putty it, paint it, and leave it at that.

The problem is the existing putty which is haphazard and very old, and two pieces of glass which are cracked (marked with red dots in the photo). I'm worried I'll crack more glass trying to remove the old putty.

I like the mismatched glass and the old sticker and would like to keep them (heritage and all that). I just have to work out how to do that.