I am a professional tig welder and used to work at a local job shop one thing that I always hate is when someone brings in a case or any other aluminum component that they have tried to fix themselves, cast aluminum is very porous and the jb weld will get into the pores and it is almost impossible to weld. also grinding out the crack is a bad idea unless you use a carbide or HSS burr. the bonding agent in grinding discs leaves residue that you cannot remove without lots of heat.the crack should be drilled out at the ends to stop the crack from growing any further and ground out so a good root face weld is possible. depending on the length of the crack you may need to put tacks every inch or so to keep the metal from moving. I like to preheat the metal before even starting the weld to keep distortion at a minimum. the best way I have found is to put it on a wood stove for a couple hours to heat it evenly or put it in an oven at 300-400 degrees or so for an hour at least. it will remove any residual oil and stabilize the metal for welding. after the part is done the temp has to be brought down slowly. I found that by setting the part back on the woodstove covered with a fiberglass blanket and leaving it overnight works very well by morning the part will be cool and should be as good as new. if you dont do the preheat you may distort the metal and cause bearing failure or poor sealing. ask the shop for samples of welds before you have it done. they should look like nickels stacked and have a shiny finnish to them if they are hazy or have spots in them think about going elsewhere. haze or spots most likely mean poor technique (too much or not enough gas flow, using improper tungsten, or holding torch to far away and trying to do too big of a pass at one time or it could mean poor pre weld prep) either way you do not want to have a leak down the road on it as it could mean a lean condition and melted down top end. hope that helps you...
