OK, my bad, looking to learn......what was the original hydraulic system? If mineral oil, I can see the O-ring swap, otherwise, I "believe" ANY DOT fluid works in ANY system (other than DOT 5 which REALLY SUCKS WATER OUT OF THE AIR).
So, you can run ANY DOT brake fluid in any DOT system, DOT 5 just means a lot more fluid changes.
So, DOT 1-4 and DOT 5.1 are all compatible.

Again, just asking for my edumafication as well as others (misspelling intentional).