Paul -- Those indentations are for the safety wiring of your drain plug to the oil tank. These indentations typically have small holes drilled horizontally through them for the passing of the safety wire. They certainly should not leak -- if they do, it may mean that the hole was inadvertently drilled into the fluid-holding portion of the tank. I would make sure it is in fact leaking before you drain the oil tank and inspect/test that area for a leak. If it is leaking there, that would seem to me to be a ROTAX warranty item. -- David
ps -- Always "double-wrench" that boss/plug when removing/tightening the assembly -- you might mess up the boss/tank bottom if over-torqued.
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B) - N124DH flying since March 2014 - 680+ hours (as of Oct 2018)!
through June 2019.