In fact, if one looks closely at the diagram, the join of the fore/aft Shafts, with its splines, is likely the source of the Oil combustion evidence in the bearing case for Second and Third Ball bearings. Here, in the Slip area, with splines worn, a rogue gas path would deposit Carbon rich deposits on the LPT Shaft (see pic). Such a "leak" would also explain loss of (some) N2.