White debris on front of cartridge

At my house it's coke.

Seriously (as opposed to my previous post), the difference you are seeing between the two cartridges accumulating white schmutz is probably only due to some difference or differences in the shape of the cartridge bodies such that one is more prone to accumulate debris where it is immediately visible. If you remove the cartridge that appears "clean" from its headshell and examine it in areas normally hidden from view when in use and under a low power microscope or even grossly, I would wager you will see white stuff there too. I have seen fine white particles on cantilevers mostly, using a microscope, but otherwise I have no idea where the residue might be coming from.

Mold is an interesting hypothesis. I just assumed it was dried wet-cleaning agent that didn’t come off in the purified water rinse. I play a lot of vintage vinyl and god knows what the chain of custody these LPs had. I get the accumulation on the front of my retipped Supex SD 909. I would think the fine line stylus would create an environment ideal for breaking off deep groove debris 

My DS Audio DS003 also gets white "Schmutz" accumulation. I could give a Rat's Arse though..These Optical Cartridge Systems are the best thing to happen to the Audio Industry since the Birth of the CD 43 years ago !

So Dump all yer ancient tech MM's, MC, MI's, Strain Gauge Thingy's an just git yerself a DS Audio system of your budget.

Schmutz won't foul the operation of an optical cartridge?