I have had the cover of my 630 twice. Its essentially the same as your 430.
Put the transmission in neutral!!!Take out the 4 bolts and unhook the neutral safety switch. Lift straight up on the shift rod until the shift forks clear the gears and then grab under the cover and set it aside. Take extreme care not to move the shifting rods at anytime between taking it of and putting it back on. DO NOT move any gears before taking a digital photo of them for reference. Check out the transmision and perform maintenance. Pull the drain plug from the bottom of the differentail/transmission casting if the fluid is discolored and milky. You most certainly have water in the section that could be causing the problems. Drain all fuids and flush with diesel. Replace the transmission gasket (which is still available from CaseIH). Refill the transmision with 90W gear oil. At Walmart in Houston, TX it was about $8.00 a gallon in one gallon bottles. NAPA has it in 5 gallon pails and the NAPA brand should be less that Walmart (about $39.00 for 5 gallons), if not buy Walmart. Pour the gear lube in the open transmission top, replace the gasket. Coating the gasket face or differential face with bearing grease before placing it helps keep the gasket in place and helps it seat. Position the gears as per the photo. Pick up the transmission cover taking care not to move the forks or shift rods and reposition the shifting forks on the sliding gears. Replace the bolts and snug up with your ratchet. Torque them diagonally to mfg. specidifcations and reconnect the neutral safety switch.