I did found a 19 mm aluminum plug last week, after I removed it nothing came out, it locates underneath the air pump on the passenger side , if it's one of the drain plugs I will give it a poke then.
99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.