@TorinoFermic
Let me explain a bit more about the switches. If you examine the photo of the inside of the one on eBay (area highlighted by yellow box) and the then look at the one that Xdevs (area highlighted by red box) you should notice that the switch for the front / rear input jacks, has no means of operating it on the eBay one, indeed the entire switch is missing. Then if you look at the power switch on the left of those photos, you will notice that the pushrod is specially shaped, so the same might be true for the input switch.
Yes, but that's not impossible for me to 3D print a new one. My printer's print volume is bigger than a half-rack DMM.
Yes, you may very well be able to 3D print a new one, but that surely requires an original to begin with in order to draw it in some form of CAD software, which presumes that the replacement switch if you can find one, is precisely the same as the original switch, which something is telling is me, is going to be unlikely. That might explain the reason for the switch having been extracted in the first place, was it used as a replacement in another meter
You asked for advice and my advice is that I personally would not touch it with a bargepole but if you can afford to write off 148 USD plus shipping if it is not repairable, then that decision is yours to make.
Like I said, I have brought from that seller before and I'm happy that they are honest people but when I got my meters from them, I paid less than a third of that price and going by the description and my own experience of the meters, I was pretty confident that I could repair them pretty easily which I did.
The 34401A does not fill me with that much confidence, the display looks to be a bit weak in the brightness stakes and will add at least an extra 150 USD if that fails anytime soon and all the other signs, for me a step to far.