Where is the most common place for a oil leak a BMW 323i

In my opinion the #1 most common place is from the oil filter housing. Stand at the front of the engine bay, look at the right side of the engine block under the intake manifold. If the block is oily, wet, then that's the culprit. There's a $5 oil seal that dries out and can end up causing oil drops on your driveway. The labor for this repair can be several hundred bucks. it takes about 3-4 hours. Other common areas are the valve cover gasket in cars over 100K miles. If you smell oil burning inside the car, when you start it up in the morning, it's likely leaking here and getting on the exhaust manifold where it burns off..
Next place to look is the high pressure hose form the vanos to the oil filter housing. It's a 8" hose with banjo fittings. Over the years they can start to leak a little. Lastly the oil pan gasket can start to leak on cars with high mileage. My 98 323is has had all four over the years. It has almost 200K on it. I've done the oil filter housing gasket and some day will do the rest
The oil filter gasket is the one that leaks the most. It's not hard to do yourself if you are mechanically. There might be youtube videos to help. Good luck.