As far as leaky injectors and cold start valve can you test that with a pressure leak down test? If the pressure is maintained then it is not leaking. As far as waiting 400 more miles, they will test it at any time, you just won't get good wear results, but they can certainly tell you how much gas is in it. But it might make more sense to wait. One thing that causes gas in the oil is lots of short trips. I used to have a 2 mile commute (the good old days) and got my oil tested at about 10,000 miles (M1 0W40) and it was still good according to Blackstone but had about 1.25% gas as I recall, and he said that was OK and caused by short trips.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra