That is certainly one way. An alternative is to rivet a piece of light angle (like J channel) across the top of the rear baffle from engine centerline to the outer corner of the oil cooler corner. The structural problem that causes the corner cracks is the flexibility inherent in the "joggle" joint at the inboard side of the oil cooler. Reinforcing the outer corner (where the cracks occur) by itself is less effective from a weight standpoint.
If one stabilizes the inboard side of the oil cooler by an engine brace (noted by others) or the baffle beam I used, the problem is eliminated without reinforcing the outer corner.
Image of described item above
600 hrs. No cracks.