loss of gears

the other day i lost my 2nd and 4th gears. i been told it may be the linkage thats flew the coop so i wondered how hard it is to fix and what i would have to do to fix it. also i put a whole in the rear diff the other dy with accidental use of a rock so as a little off road repair i used some bathroom silicone i had in the boot and it worked a treat not leaked and it got me home without any drama and was fine driving around for the next day till it got welded