I have been trying to find all the tapes and guns by myself but I just can't find the Eulenberg #2 and the Jim #1 tapes also where are the blueprints for riveter and auto shotgun I've looked around the map like 2 times and I still can't find them.

I'm at the end of the game, and I've been combing through trying to get all the secret cassette tapes/weapon blueprints. Things I know I'm missing: Eulenberg #2 Capt. Solis #1 Kahn #1 The room by the tram with the red light and red X on either side. The locked room to the right of the Omega boss. If anyone has figured some of these out, any help/hints are appreciated! I've been having a good time searching, but I think I have to throw in the towel on these ones....

Please let both happen.

It is the only blueprint I need to get all the achievements, and I have no idea where to find it. Any help would be appreciated!

Is there a way to return to the previous areas if you are that far?