Advice on possible AC condenser replacement

Hi everyone! Slowly working my way through my maintenance list - now onto the AC (it's 96 F here today...).

When I bought my 2008 a couple of years ago, the AC worked fine for the first summer, then when the next summer rolled around it blew warm. I had a mechanic recharge the system and it worked for another summer.

Well it's summer again and the AC is blowing warm again. I figure it's time to track down the leak.

I had a peak under the hood at the various refrigerant lines. None of them looked black / dust caked / oily / wet, just shiny silver.

I also had a peak at the condenser. Photos attached. The bottom left side looks dark / dust caked, like there has been a leak that has captured dirt. The line running into the bottom left is similarly dust caked, like something has leaked down onto it. The rest of the condenser looks silver / relatively clean.

Am I crazy in thinking that the condenser is likely the cause of the leak? If so, it seems it is a relatively easy replacement, followed by vacuum + recharge by a mechanic? I believe there is little to no refrigerant in the system at the moment (B1423 code).

I guess it would be conclusive to have a mechanic put dye in the system, but I was hoping to avoid paying for two recharges...

Any advice / suggestions?

If replacing the condenser first is the way to go, is there a recommended alternative to ND-11 oil? I see a few "hybrid compatible" oils available online now.