Well, it's cracked. How bad is it?

I wouldn't, because even though the block is metal it is permeated with oil and glue's will have a hard time staying there and end up in the oil to get sucked up and pumped into the bearings.

I would SO reach in there and snap off that piece from the crack around towards the crank with a pair of needle nose then red RTV the new stick tube in and run that thing for 20 years.

I'd snap it off intentionally so it didn't snap off later and possibly get taken up by crank windage and get somewhere disastrous.