Actually, just checked catch can. The last 250 mile motorway journey for the first time has collected about 30ml in the bottom of the can. Mostly watery, with some oil.
Fuel dilution doesn't increase linearly with miles. Furthermore, oil level would go UP if your example was the case, as the fuel dilution would add volume to the sump. What actually ends up happening is the oil releases the fuel vapor to be consumed by the PCV system, as well as any other low pressure vapor liquids. The rate of dilution eventually matches the rate of vaporization of fuel in the sump, and you reach a fuel dilution equilibrium. I've tracked vehicles that had fuel dilution for nearly 40,000 miles (on a single oil change), and observed the fuel dilution trends during that time; it is not linearly increasing.IF that all checks out and nothing gets worse I may live with it, keep it topped and just change oil at 3000 miles like some others do on here. Clearly the oil will thin as more fuel dilution happens and consumption may go up.