The Japanese Soryu-class have one big problem: politics.
No country can be sure about the future Japanese politics according to weapon exports like spare parts. Also Japan has no experience in exporting military hardware and adopting it to customers needs. The same error Australia made with Kockums. Kockums did build marvelous submarines for Sweden but had no knowledge how to export them.
The Soryu-class is big but has less range than current Australian Collins-class. Japan has less need for range than Australia.
I prefer rather small submarines like Type 210mod and tenders to extend the range. For one Virginia-class submarine you can buy about 8 Type 210mod and men them all with the crew size of one Virginia-class submarine!
What do you think would scare China more:
One Virginia-class submarine
or 8 Type 210mod?
If the Aussies were to go with the Soryu-class, I'd expect they'd want to build them in Australia to prevent the kind of spares problems you suggested. They might enter into a co-development with Japan to improve any of the Soryu-class identified problems.