I just spent ALL DAY yesterday working on my landing gear. I had a replacement unit I purchased from Dormar (
http://www.domarproducts.com/gearbox.html ), but the leg measurements proved to be different from the Venture ones, and the leg bevel gears were not interchangeable. I do think that the Domar is heavier, and better made, but I am on the road and didn't want to mess things up. The Domar reduction gearbox is metal, where the Venture is plastic.
Yes, the generator removal is going to be a bear, and I suspect you will need lifting help at least. I just had "generator prep", and had to get the metal shell out of the way. The screws for that are pretty straightforward (center divider and along the bottom edge), but I couldn't figure how to get it out. I finally ended up moving it side to side as I worked on the left and right legs.
You will probably be using the manual crank some to get bolts/nuts on the connector shaft into the right position for removal/replacement. You CAN remove the drive leg with the motor gears in place, but it is heavy and in a confined space. I removed the motor from the leg in place, and found that the gear motor assembly that simply slides over the leg shaft through a D shaped bushing/gear got caught in burrs in the shaft. It took some prying and hammering through the crank access hole to get it off. Out on the picnic bench worktable, putting the new metal gearbox on was just as difficult, for the same reason. I got out a file to smooth the burring on the shaft and it took several attempts and some grease to get it to slide together. I re-installed with the motor/gearbox assembly in place and was really fighting the weight to get it up and into position. I added up some folded up electrical tape as a spacer/cushion on the gearbox/leg retainer points to take up the gearbox rotational slop. I ended up using a 2X4 lever and fulcrum foot lifter along with levelling pads to raise the assembly. Also, wiring up the motor and letting the leg lift itself by extending, helped lift it into position before bolting it down.
After I finished this leg I found that my off door side leg is completely locked up - won't go up or down. I ordered a repair gear set from the Lippert online catalog last night, but it won't get here for a week. Then I get to fight removing the other leg.
Good luck in your effort. Oh, by the way, I hitched up to support the rig during the repair. This might not work for you if you are removing the generator, and will need a jack and jackstands. I couldn't see the frame jacking points in front, anyways.