I own a 3414 with a 3120 backhoe. It is officially my stumpdigger. It is a pretty decent machine. My electrics were hosed up on mine when I got it. Someone didn't really know what they were doing with the wiring and it was a battery drainer until I rewired it.
I ran it for awhile and it started to slip a bit lately and I finally discovered where the tranny oil level check is - was low... check bolt was covered in grease and dirt. Hopefully I didn't wear the clutches down as the final drive gasket on one side needs repair/replace. The transmission needs oil.
Take my advice. First thing when the weather allows, get the thing cleaned up with some engine degreaser and a hosing off and go through the wiring - get an operators manual. I fixed the wiring and now the glow plugs actually work as well (just rewired correctly). The manuals are about 30 bucks.
The machine is very heavy and lacks ROPS. Mine, with the hoe is about 9,500 pounds per the hauler and scale slips.
Mine is a diesel and starts without ether now that the glow plugs are fixed, but I don't keep it out in the winter or use it at all. At least in the diesel, don't want to run it empty on fuel, cuz you have to go through a manual pumping procedure.
If you need any help, you can msg me and I'll do my best, but I'm not a mechanic.