Thanks Deejay, the sole blade has a raised lip on the cutting edge, I will have photos next week, they are common on industrial mowers, they are more robust and last longer.
As for air flow through the side case, I can always machine up or retro fit a breather, but I dont think it will be too much of an issue as I regually remove the side case and clean/re-grease and inspect...time will tell i guess.
