I'll bet that you are using Synthetic oil. If so, to get a correct reading you need to let the car sit overnight before measuring the level. This you are doing so that's OK.

The puzzle comes as to why it showing a lower level after you measure it overnight for the second time. One possibility is that you are wiping the dipstick with a Kleenex, or something else that makes it slippery and that does not let the oil stick to the dipstick properly. Wipe it again with a rug and let it sit for about 5 minutes before taking another reading. You should then have a correct reading.

Been there, done that.

Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]