It can sometimes take a couple of attempts during reassembly to get everything working properly. Make sure to review all of the installation notes in the guide and to check as much functionality as possible after each piece goes back in. If you want more details about the mirror box, check out the mirror mechanism guide. It has a video showing the mechanism in action. If the shutter button is not working after reassembly, the mirror box is a good place to start investigating. That is what the shutter button fires first. Then the mirror triggers the shutter release.

Thanks for the advice on the weather sealing. I've only heard of one shop being able to replace the seals but I've wanted to experiment with some "home remedies".

In your other comment you mentioned having some bodies with the always on failure. I'd like to ask you some questions about them but iFixit doesn't have direct messaging. Are you online at any other forums where I could contact you? I'm on pentaxforums, photrio, and reddit mostly.

Yeah, I agree. It sounds like the "decrease" button is stuck. Since you already investigated the button itself, I would look into the contact between the top cover and the body. The decrease button communicates to the camera through the middle of those three contacts. If that contact is shorted to ground, it will act like it is stuck down.

I would check out the replacement guide for the ZX-5n. The construction of that camera is more similar to the MZ-30. Some of the wiring will be different but just take some pics for reference when reassembling. The parts page has a link to a place where you can order the gear or you can use the gear specs to search for parts on eBay and Aliexpress.

Pentax ZX-5n Mirror Motor Gear Replacement

It's hard to say precisely what the issue is but my guess is something around the aperture set lever. Unfortunately, I think you have to take it all apart and put it back together. Sometimes you just miss something. I would double check steps 32 and 33 and make sure those are followed during reassembly. You can also check out this video for a more in depth description of how the aperture mechanism is supposed to work. It might point you towards a more specific area.

https://www.youtube.com/watch?v=4V3x1cm-...

My first thought is to make sure you are testing the speeds with film in the camera, although this can be a bit tricky with some testers. For the slow speeds, like 1s, the camera measures the light off the surface of the film and calculates the proper exposure in real time. Without film loaded, it measures the light off the pressure plate or whatever you testing unit puts in the film plane. These are usually "darker" than film and result in artificially long shutter times.

No, the manual speeds are not affected by the variable resistors. If the manual speeds are off the first step is to service the shutter (i.e. disassemble and clean the shutter). If they are still inaccurate, there is an adjustment screw on the shutter itself but it is difficult to use properly. And it's more useful for adjusting the fast speeds rather than the slow speeds as it changes the release timing of the closing curtain.

It should be. I haven't done it but it is a separate piece from the plastic panels. Try applying some isopropyl alcohol along an edge to soften the adhesive, then work a dull scraper underneath. It should come off without too much effort.

You're right. I originally included the top cover disassembly because that's the order I use for a more complete disassembly but it's not necessary to get the front cover off. And thanks for your comments elsewhere in the guides. I mention on the main camera page that the guides are for the 23102 models (the mid/late models) but it's good to have more specific notes about where they differ from early models.

Honestly, I can't say what their specific purpose is other than some sort of damping. There are still two larger rubber bumpers on the bottom of the shutter that catch the edges of the curtains. Those do most of the work of stopping the blades without damaging them. I've tried both approaches, replacing the dampers with homemade parts and leaving them absent, and haven't been able to identify any differences in performance. The recommendation to leave them comes from that experience as well as comments I've seen other repairers make when they service this shutter. From what I can tell, they are supposed to be T-shaped and about 1 mm thick, in case you want to make a replacement.