Is vehicle's fluid level monitoring the best way to detect all leaks?

Question

I did an oil change for my friend's car and the mechanic was trying to convince me that it is leaking oil and brake fluid. He suggested that the car needs a costly repair (~$1400).

While I don't have a reference for the oil level before this particular oil change, I rechecked the brake fluid level and it was still at MAX level. The last time the brake fluid was changed was a year ago. The only thing that looked suspicious to me was a little bit of engine oil on the engine, but seeing oil somewhere one the engine does not necessarily indicate a leak (e.g. possibly it could have been careless oil change that resulted in spills on engine in the past).

My question is - If a mechanic tries to convince you that a car is leaking something (e.g. oil, break fluid, coolant) and the particular fluid level actually had not changed over several months, is this a good indication that a car actually does not need any repair in the first place?

This is 2008 BMW X3 with gasoline engine.

Edit:

Here is how approximately quote looks like:

1. Oil Pan Gasket
1.2. Replace
1.1.1. Auto Trans (B)                 $760
1.2. Pan Gasket                       $37
2. Pan bolt set                       $28
3. Cleaner                            $16
4. Break vacuum pump unit P/L         $700 <-- Added later with pencil to quote

Answer 1

There are a couple of tactics you can use to detect oil leaks on engines and transmissions.

First, get all the oil off. Some use a water soluble degreaser like gunk or simple green. Whattever works and doesn't destroy the planet.

There are many debates about using a power washer, I WILL use one. If you choose to, be mindful of wiring and seals.

Once the oil is removed and the water has evaporated through by going on a short drive use some talcom powder or similar substance and throw it onto areas of the motor you feel might be leaking. You can use a leaf blower or compressed air to remove excess powder. You will see remnants of the powder you use sticking to any fluids such as brake fluid or oil and determine yourself whether or not an oil pan gasket is in order.

I have been tricked by oil remnants in the past and have changed a pan gasket or two when in actuality it was a front main seal dripping down onto the pan thereby fooling me into thinking it was a pan gasket when it was not.

Hope this is helpful. Good luck.