300 fourtrax 4x4 front driveshaft problems

Welcome to the forums , I would guess when the wrong gen shaft was slipping , it damaged the splines of the front diff

yeap , I wasn't even thinking about what Mac said , it sounds like you have a stripped input spline on the front diff ----I have a 96 frame with a 92 engine in it , but I replaced the front shaft with a 4x2 kick out , once the anti-rotation strap of the 4x2 got hit jumping a stump or root and slide the assembly back and the front diff would click and go in and out , lucky I didn't strip the splines , but just a short time and I could see the worn spots on both the shaft splines and the diff splines ,so if yours was ridden for a while like that I would be the damage is severe , but the damage might be on the end and you might be able to clean the splines up with a file or Dremel and get by this problem

yes it could , the spring on the front shaft should be on the transfer case side pushing the shaft forward , same on the rear drive shaft

with a 96 frame the Wide Open 4x2 should drop right in , it is the 1st gen frame that requires a mod to the 4x2 for it to work