Leakage

Yesterday I bought this car from a dealership with good reviews on many car buying sites. The Carfax is clean (no reported accidents). Other than a few scratches here and there, the car seemed to be fine. It also passed NYS inspection (including emission test) on the same day.

Today, I brought the car for a quick oil change and estimate on full timing belt service (it is an old/used car after all). I asked my mechanic to take a look at the car make sure everything is good underneath the hood.

He found several minor issues such as missing drain plugs under carrier, missing driver engine side cover, air filters, wiper blades etc. Minor stuff for the most past and cheap fixes.

However, he found 2 "major" issues,

1. He found a pending code P0455 Evap emission fest (gross link). What does this mean exactly? He told me that there is a problem with the emission system and eventually the check engine light will be on. He does not know the exact problem because EVAP test needs to be performed.

2. Small/minor oil leakage. He told me the gasket needs to be replaced and he quoted me $470.00 for this. My mechanic said the car passed the NYS inspection because the leak is not "major" enough. Picture of the leakage (attached below).

3. My mechanic suspected the car may have been flooded due to the missing drain plugs and the fact the bottom frame of the car (it is hard to see when the car is not lifted) has been replaced. The Carfax record for this vehicle shows no accidents/flood/theft issues. I have checked with several other similar sites. Is this a possibility?

I have called my dealership and they said to bring the car on Tuesday to their mechanic (holiday weekend now) and they will honor their thirty day warranty on engine/transmission.

I just wanted to know what you guys think about this? Did I accidentally buy a flooded vehicle? Or these are just common issues that come with buying used vehicles?

Thank you