Since the cooler inlet temp is an average of all the individual scavenge temps from crankcase, rockers, etc. there certainly will be some scatter among these temps.
If you're genuinely concerned about localized hot spot temps why not ask Lycoming for their advice? They must have a good idea what the hotter areas are likely to be, and how to measure them.
Once you know the cooler effectiveness you'll have a good idea how much margin exists. (Dumb questions - is the 118 redline for supply, or for scavenge? And what ambient temp were you running?)