I hear a grinding sound not unlike a kettle boiling when my 2WD Saff cruises in 5th and sometimes in 4th. What is the problem?

I spotted some oil leak just in between the gearbox and the shaft. Can I get away with it just by changing the oil seals or do I have to buy a new prop shaft?

Or is the gearbox damaged? Time for a rebuild?

Thanks in advance!