I have no confidence in the shop you have your bus in.
We had a temporary drop in confidence when the serial number / model number mismatch had them confused for a bit. But though their part guy was completely lost, the mechanics weren't and they do have several genuine two-stroke guys on staff who have seen plenty of engines like ours.
Overall we are (so far) impressed with this shop. Despite being a big shop with 14 bays (and a relatively pricey shop rate), they haven't pressured us or rushed us at all. They are happy to let us live in the bus while we are here, even while they are working. They are willing to let us watch and learn and be involved as we dive deeper into the engine. They have encouraged us to do our research, and to consult outside sources and other options. They are actively interested in hearing about alternative ideas that we have come up with. And they are even open to helping us relocate elsewhere if we decide that is best.
All these things inspire confidence. And we've heard from several bus nuts who have had good (though perhaps not cheap) experiences at this shop too, and no one with a bad first hand experience yet.
So... What reason is there to lack confidence?
That they haven't gone any further doing diagnostics is at our request - based on the advice we've gotten from the shop here, and from many others we have consulted with. We aren't in a rush. We aren't far from home - we are home. We have electricity and internet and shops and restaurants and even hiking trails nearby.
We are very happy to take some time to weigh our options before racking up shop hours.
It is the smart thing to do.
And that the shop hasn't been pressuring us at all to start giving them more billable work is the most confidence inspiring thing.