I love all the responses! Thank you all so much. Life is pretty busy as I'm renovating my apartment but I managed to take a look at my bike one more time after reading the responses.

1) The bike mechanic at a bike shop was mistaken when he said the fork was aluminum. It's not -- it's steel as confirmed via a magnet test.
2) The bike mechanic did correctly use a Park Tool fork alignment tool and it showed the forks were slightly off horizontally and vertically.
3) I cannot verify what tool the bike mechanic used to measure the rear dropout -- it did involve some sort of gauge.
4) Please note that the bike mechanic did not even attempt to sell me a bike -- he said it's simply no good.
5) The bike mechanic refused to repair it, only if it were steel he would. I called another shop and they refused to repair aluminum for liability reasons. Seems like I'm left with little choice but to do the alignment myself and attempt to fix it.

To confirm that something was bent on the bike, I already looked at the alignment of the wheel against the frame and while very, very hard to see, I can tell that the way the front wheel aligns up against the bottom tube is a bit off. I already rode the bike without my hands on and I do see the top tube leaning to the left. As for my left leg overworking, let's just say that I had experience unknowingly riding a touring bike that I crashed at one point. For thousand of miles, I thought everything was fine until I noticed that the bike liked to lean to the left (just like the Cannondale). When I eventually learned how to ride my bike without hands, I had to position myself oddly on my saddle to make the bike go straight. I later developed osgood-schlatter disease on only my left knee because of overworking my left leg so I can continuously go straight. I definitely know the dangers of riding an unaligned bike -- it goes beyond safety, it impacts your health as well. But come to think of it, it seems like every bike I ride leans to the left. It could be just pure coincidence.

Since I have five bikes with all of them being vintage, maybe it's time to invest in a Park Tool. Too bad they cost $65 bucks. Better than paying the guy $25 repeatedly for each bike.

More updates to come if time allows.