Some eejit on the tube yesterday fell into me and as a result I ended up crushing a nice, fresh pear (part of my healthy lunch) that was in my MKVII. The pear then "leaked" into the wee pocket and along the side wall of the MKVII.
I know some substances can be harmful to old fabrics (it is an original bag), so does anyone have any advice? It isn't a large area affected, and to be honest you can't even see where it happened anymore.
I think you're safe, and so is your bag.
A lot of the used bags have had stains of 60 year old oil, rust, dirt and what not and they have survived just fine.
I'd just try and rinse it in some water, or leave it alone if it's not bothering you like you suggested.