Yes. My engine for the S-21 only has parts in it that I could not get from elsewhere. I had to get the slippers, valve springs and cotters, studs and various shims and thrust washers...this totalled $2500 !!!!
The rest like roller bearings and gearbox bearings and all seals and Orings, the valves and pistons and cylinders were from the big bore kit all have been obtained from elsewhere and mostly are even higher quality that supplied by Rotax
Engine rebuilds can be done at a far better reasonable price if you know where to find stuff. I have a mate who is in a business that deals with all sorts of mechanical stuff and is a whiz at sourcing all this stuff. Oc course you cant do this with anything certified but for experimental or 19 rego its not a issue and you literally can save 10k on a rebuild