I did think of that but that sort of drain is very high. and it seems not to be constant.. Symtoms seem to be the same tho', yours in hot weather mine in our current white stuff

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1990 124, 300E 2.6 (daughter)
2004 Cayenne S, Fabspeed Cat Bypass, BMC Racing Filter
2000 Lexus RX 300 (Wife)
Retired 1999 ML430