In the 75,000 miles I put on an A between 57 & 65, I adjusted the rod & main brgs 3 times.If you keep the cruising speed around 45,dont lug the engine & service the car regularly,they will last a long time.I always cruise at 45 or 60 when in OD.As long as the engine has no bearing noises,then no need to drop the pan.A main brg will generaly be a pounding noise when going up hill,while a rod brg will rattle when you let off on the gas.A leaking rear main is also a sign of too much clearance.