Hardware questions of HP-67

[Waon Shinyoe]

Just acquired a heavily corroded HP-67. After some cleaning work with vinegar and alcohol, I have the following questions:

1. What's the use of those shiny metal contacts? (Please see the attachment)

2. The keys B, GTO, g, and ENTER don't work. They are on the same column, so I doubt what can cause such problem and how to repair it.

3. Since the battery terminals are all gone, I soldered wires and installed a battery box. However, if I use batteries instead of AC power supply, the power on LED would blink once, but there is no display. I check the wires and I'm sure they are connected to the contact points of the AC power port. (BTW my multi meter was broken these days I will update the post once I acquire a good one. )

4. When I use AC power, I have to press the ON/OFF switch hard to keep it on. I thought it might be a problem of assembly, but I didn't find anything wrong.

Also, is there anything like a service manual? Thanks a lot.