OK
Why do you think you need a C4?
That "made in poland" bearing wasn't a C4. The C4 would be part of the part number etched into it. 6004 N-C4
I can't think of why you would need a C4 in the transmission of a bike.
... and your transmission shaft isn't spinning any where near the RPM rating of a open 6004 bearing.
... and when you're installing bearings ALWAYS install them with the writing out.
Where have you tried to get this bearing? that sold you the wrong chinese bearing... (There's nothing wrong with VXB bearings, but if you're going to use 2R bearings with the seals pulled off in oil, wash the grease out of them. You don't want globs of grease floating around the transmission oil).
Call RBI or Canada Bearing on Tuesday.
C4 = high internal clearance. https://www.jesa.com/en/wp-content/uploads/2016/07/Tableau-1-EN.png
SKF
www.skf.com
Minor digging through parts diagrams suggests that C4 is indeed what is specified ... but it isn't what was in there!
The motorcycle is at a friends property and I did not take out the bearings last time I was there taking apart the engine. Once home I decided to follow the advice I received online and replace the main & counter-shaft bearings as they were exposed to load while the counter-shaft was broken. For most of the bearings this wasn't and issue as I was able to order it by the KTM part #. This last bearing they could not ordered. in the parts diagram the description for the part is "BALL BEARING 6004 C4 N So I was going based on that, and I don't know what N specifies but the first time I searched with the N it came up with NTN bearings so I thought the N in the description is a cut-off NTN.
Last night on another forum someone suggested a KTM parts place in Europe. I ordered the part and was notified they will have it in 2-3 days. I guess KTM dealers in Canada do not check with Europe and I took their word that it was discontinued and unavailable. I hope after 10 days of waiting I am not met with a wrong part =). May try to source one locally with a groove just in case.
Thanks everyone for the help.