It's not just the oil. A mechanical watch needs to be disassembled and its individual parts cleaned of lube, microscopic metal particles, dust and other things I'm sure I haven't listed. Disassembly is done by hand, and the cleaning is done by soaking the parts in a cleaning solution and perhaps ultrasonically. Parts that are worn out, damaged or corroded need to be replaced or possibly repaired. The newer lubes are superior to some from the past, but they need to be applied to specific points in the movement as lube is detrimental in some areas. I'm still a newb at this subject, so hopefully someone else will chime in.