Not a problem what so ever!
The drive motors don't connect to the sprockets directly, they go through a reduction drive first. They fit into a matching spine to engage, you more or less have a direct connection (speed wise) to your park brake disc's, so your brake actually holds the power the drive motor puts out directly not after it has been reduced which means they can use a smaller brake setup.
The drive motors are VERY simple to remove. Remove the 3 hoses, then remove the 4 bolts on the motor housing to the reduction box. Simply pull the motor out and it will disengage the drive spline. The cover does absolutely nothing but to protect the motor and make it look *pretty*. Damaged covers will not do a thing to loose oil, they are just covers that bolt to the chassis with 4 bolts. The sealant looking stuff you see on the outside is just rubber to fill the space between the chassis and the cover, there is no seal underneath. If you are leaking chain case fluid, it could be the O ring between the motor and reduction box but if its on the right side (while sitting in the machine) it may be your control block seals. This design was common from 743/743B and earlier, my 731 had the exact same setup for the motor mounting.
I will try and scan in details of this at work tomorrow, it is very simple. If you want to e-mail me direct, check my e-mail in the user profiles. Unfortunately i know FAR too much about 743 machines.....
If any of that isn't clear just yell!