Gearbox Inspection cost depends on parts used and the extent of the inspection. Calendar age and hours along with extent of previous inspections also very price. A gearbox on the bench typically takes 1-2hrs to disassemble clean and inspect. If the bearing and seal are replaced, that will add about 175$ in parts. The 3 disk springs should almost always be replaced with a few exceptions at $75. Gearset, thrust washers, clutch hub and prop shaft can increase cost if fracturing or wear is detected. Your clutch may be due for a cleaning and adjustment and that adds 1-1.5hrs of labor.