My RB67, along with three 120 backs and my 65/90/127/180 Sekor C lenses recently survived a bike crash where I fractured a rib and got road rash and cuts from my face to my knee. There's blood stains on the canvas bag all of this gear was in.
I guess this is the bit where everyone weighs in with "I've been using X for decades and it's perfect!" (an RZ67 for me, but only ~6 years). Probably not many people have used multiple 6x7 systems.
It's all a matter of risk analysis, which risks your usage poses to the camera and which risks you can tolerate:
- an RB is mechanically pretty strong, but the shutters will become inaccurate and require CLA
- an RZ is nearly as strong as an RB, and lighter. The shutters are perfectly accurate (nice if you shoot chromes)
- the electrical connections in an RZ can be flaky wrt metering. Dirty contacts (back/body and prism/body) can cause bad metering results, but I've never seen a bad contact prevent the camera from operating
- a Mamiya 7 is light and sharp and wonderful and expensive and do you really want to get it dirty?
Ya need to think about which features and risks you care about and ignore a bunch of people on the internet who've probably only used one thing. Pentaxes are meant to be reliable and they have a really nice lens selection, so I second the thought of looking at a new repairer if the camera and its features suit you.
use a TLR if you need reliable and can take the bulk a mamiya if you need interchangibility or straight film run.
Step back or crop less.
If you are in a studio and your instant film shot is bad spit on the RB and shoot with the TLR.
Lots of advice! I don't know how much to add but I have owned and used a variety of 6x7 cameras.
RB67 Pro Sd
Mamiya Press Super 23
After a few years with each, I have settled on the P67ii but have only had it for a few months so can't say much. As for the others, my next favorite was the GS-1 for its portability, great lenses even though it had a minor winding mechanism issue. But alas, I recently sold it and even though it worked fine for me, upon arrival at the buyer's doorstep it developed a problem that is requiring repairs! All of these cameras were purchased second hand and I never had any significant mechanical issues with any of them.
Since you seem to really like the Pentax system my suggestion would be that you send your Pentax in for repairs and I strongly recommend Eric at pentaxs.com He is very good at what he does. If that fails then look for a GS-1 in good condition. The RB was just too heavy for me even though it was a beauty and I loved the fact that it didn't require batteries.