its often not even soldered, I am convinced some of these parts they get the connector or terminator with a little tab sticking out, put a dash of glue into place and stick it inside. Isolators seem to have a trapazoid/wedge geometry in them that aligns the little tab correctly.
I was able to repair an isolator that had a dented SMA connector on it by ripping it out, then screwing a new 'short tongue' wave-guide W40(?) sma connector with a tiny dash of silver epoxy on the tab.
I don't know another assembly method ( other then cutting it open, conventional solder and welding, totally heating the thing up with solder paste or some kind of interesting laser optics/pnumatic clamp. ). I think its just designed with glue.
The thermal time constants of all the parts to be soldered are so low, I was not even sure you can do it if you heat everything up with a laser and smash the thing together at the smallest gap which would allow a laser beam to heat the stuff inside. MAYBE if you got a bus-bar and heated up the whole thing to make a ultra thin soldering iron you can do it, but I have a feeling that if you assembled it this way, then tightened the screws, it would not be a reliable joint with out some kind of precision alignment to let the solder solidify in the correct space.. it would be under tension/torque.
I would recommend ultra high conductivity silver epoxy.
The circulator displayed above.. is pleasant. Mine was totally welded around the perimeter, and nicely painted. The amount of work that would go into restoring it would be ridiclous.
If I was sure that you can heat the whole thing and use solder paste without cracking anything, I would do that, but I have no idea what the reflow (cooling) profile would be... maybe low melting point solder. IMO don't bother unless you have a mechanically damaged one.
I do think the one above is built a bit bootleg, since they use a standard SMA connector with a solder barrel, rather then a waveguide insertion flat tab. That looks like its meant to bond to a wire not make a solder lap joint. I suspect that the inner pin is going to be less mechanically reliable with thermal variations then the (more) proper type..