Could be that the handful of AC units I've seen removed were improperly installed. They all had the rear foam strip attached. The only way I could see causing a leak is if it were to thick and interfered with the compression of gasket. Only using it to limit free movement of cantilevered end, pan may not need it but at least in my eye, my roof wouldn't resit the leverage. Many replacement gasket kits come with extra strip(s)?
The smaller dense squares, Ive only seen mention as a means to prevent over compression-though they are so thin cant see how that works.
If a phone call was to be made wonder what Dometic might suggest (or why the extra strip was included with mine). Curious
Noted on the newer NLs raised areas on roof under AC- if AC doesnt make contact what purpose would they serve?