saad bhai what do u say about this ...
damage due to gear oil overfilling
The fluid may foam and Froth and form bubbles due to contact with air, and that can lead to erratic gear shifting(slipping / unable to shift ). Other problems can include transmission damage and oil starvation. Leaks from the vent and the gear trains slowing down when the clutch is depressed, leading to gear shifting problems.seal failure may also occur.
Too much oil in a gearbox will cause the gears to "churn" in the oil more than necessary and create heat which can be excessive and beyond the capabilities of the respective oil cooling system to handle (i.e. oil coolers, air flow cooling over the case, etc) and result in thermal runaway of the oil. In extreme cases the internals can reach temperatures that will cause distortion/melting. It can also cause to much aeration in the oil which could be more than what the stock breather system can handle, which will reduce lubrication capabilities (foamy oil doesn't lubricate well).