Search the thread, using key terms 'gearbox', 'gear oil', 'engine oil', 'gear', etc. There are some useful posts previously.
Check if grinding occurs with engine off too. The sounds from gear box reduced very much after gear oil change to specified one. Previously it had thicker oil creating problems.
I replaced hubs too 900 each. My wobbling has gone. Sometimes aftermarket discs need tooling before installation, as shopkeepers drop these things on floor violently.
Add coolant very very slowly. This allows less air locking. Maybe your water pump is dead. I once had my generator belt broken and engine heated upto 60% gauge because water pump works with the same belt.
I got gearbox repaired for 6000rs. As kabli ones were around 15000rs.