I've put 50000km on mine on dodgy Australian roads without an issue, and I've not heard of the sump or oil cooler being damaged on any of these bikes. I have however heard of two speedmasters having their oil filter taken out by road debris which can quickly kill your engine, so if you're concerned about this that's what I'd be fabricating a guard for. If you decide to do something with the oil cooler be careful not to reduce the airflow to the cooler or the cylinders behind it.
