You guys are throwing every excuse out there. Maybe just admit a defective product? Nah...
It's the customers fault, as always
A lot of us do our own oil changes with the stock plug and never have an issue. Seems like LN plugs leak if you don't get them tight enough, leak if you use correct torque and crack and leak if too tight.
That points to a bad product. You say it's not common, yet I've read more reports of leaking LN plugs over the years than I can keep track of.
Good on you for offering replacements, but quit blaming the customer and own up.