Magnificent Diamonds

Hello, I’m in the process of constructing a Zubmarine and am in need of five more magnificent diamonds. I’ve found there are two likely options here: expeditions in the Forgotten Quarter or getting lucky diamond bags from Empire Adornments. Which of these is more efficient? Bulk diamond purchases seem like they would be more action-efficient if I already have the clues, but if the probability is extremely low it could just blow through them all. The action cost of expeditions is higher, depending also on which one I choose - is the thieves cache as likely to give me diamonds as the Shrine? Less? More? It’s all a mystery to me.

Thieves’ Cache should be give roughly twice the chance for diamonds, since I believe that it’s restricted to about half the range of the shrine, and the diamonds happen to be in that range.

Well, this is working out perfectly. Two thieves’ caches later I have gotten 4 of the 5 diamonds I needed. Thank you for the tip! Looks like I’ll be back in Wilmot’s End for the whirring contraptions sooner than I thought.