is it normal for these aircraft to have oil on them
Radial engines leak oil, during military training it was said, tongue in cheek, if you could step over the puddle of oil on the ground it was only a drip. See some operators at at air shows have reused tins from the kitchen to hang below the known leak points to collect the drips and prevent fouling the tarmac. In the hangars you will see drip trays on the floor adroitly positioned.
The photo in the report however suggests the leak was not normal.