I have a small stress crack I noticed over the weekend. I threw a blade about a month ago and I assume it clipped the drive and cracked it a bit.

Can this be welded or will I have to get a new housing if it gets worse?

Need pics buddy and what are u running it on

I tried to take a picture but its such a thin crack it doesn't show.

42 fountain poker run with 525's

It will depend on where the crack is and if it goes all the way through the case.

Its at the top in the corner where the bolts are. Ill try to take another picture tonight

I would think it should be able to be welded then. As long as the crack is not going through the case to an area where there is torque or stress from bearings or gears it should be fine if repaired correctly. You might want to see if Doug at OPC or Andy at PBC can look at it. They will know for sure.
They will most likely have to at least split the upper and lower to inspect it.

I wouldn't have any qualms with repairing this at all. Find a local competent TIG welder, make sure the case is very clean inside and out and have him go at it. If the crack is visible inside of the case be sure to have the welder not only "V" the crack out, but to drill a very small whole at each end of the crack before welding it up.