If fluid went between the inner and outer cartridge wall during filling due to not being injected directly into the fill hole (or overflowing from the fill hole), this is fine and won't effect the cartridge function. BUT, if the fluid is there due to a leak in the inner membrane, this would cause problems with the cartridge. To check, you can carefully remove the plastic side wall by pulling it straight off the cartridge body with your fingers (don't use anything to pry if off, or you could easily puncture the thin membrane under neath). Gently wipe the inner membrane and outer plastic wall to clean off PiezoFlush, then check to make sure the inner membrane isn't leaking fluid before reattaching the outer plastic wall (make sure it's flat and fully secured before installing the cart into your printer).
Please let me know if you have further questions or there's anything else I can help you with.
Best regards~ Dana