Hey guys when I took my X5 to my indy last year, he stated that my car's driver side rear diff seal was leaking, but when I went underneath the car today I do not see any visible leaks and I have never seen a leak spot in the garage. Based on the pictures do you guys see any signs of a leak or past leak? (The first two pictures have flash, the last one has no flash).

Also, my car has 107k miles and it has never had a transmission fluid change and I believe it is time to change it per BMW's service manual recommendation and sometimes when I change from low speed to high speed there is a bang (pretty sure its not normal) but I have read the sticky thread and some are saying it's too late to change the fluid because the new fluid could clean and move contaminants left in the valve body and cause damage due to blockage. Also if I know that there is only 40% of oil in the pan, so how do I flush out 100% of the fluid? Should I bring my car to the indy to flush the oil and fix a leaking transmission electrical connector (even though I don't see any leaking) or could I just flush the transmission myself? Thanks in advance!

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1990 BMW 525i
2004 BMW X5 4.4i
2011 Toyota Tacoma Pre-Runner V6