First the disclaimer:
I have direct personal experience with this issue, but that doesn't make me an expert. I am not a professional mechanic, but I have serviced several sets of FJR forks the past 20 years. I did not spend the night at a Holiday Inn Express.
This is a recurring problem with the 2013 - 2015 front forks. Has happened several times in the last couple of years.
There are several options available.
But first scroll down to the bottom of this thread and you will see several other threads about the same issue.
There are some options listed in some of those threads.
1) Least expensive and most hoped for - Maybe someone on one of the FJR forums (or maybe FB forum) has upgraded their front forks with replacement cartridges and still has the original cartridge internals in the garage and would be willing to part with them. You'll have to ask.
2) RaceTech has a Gold Valve Kit that replaces that compression valve with a new piece that also gives the advantage of custom adjusted valving. Coupled with new springs would be a reasonable upgrade. You can probably do it yourself (well, maybe not, you already broke one
) or send it to RaceTech and have them install it.
3) Yes, a new 2016 and up complete right fork leg will slide right into the clamps and function exactly as the original fork leg. The cartridge was redesigned in 2016 and up to make them cheaper to manufacture, the compression valve is press fit into the cartridge making them permanent and not replaceable (well maybe a suspension machine shop could do something with them). Not sure if the compression valve shim stacks were recalibrated or not. Not sure if the 2016 and up cartridges will fit into the 2013 - 2015 fork leg there are some differences in the parts list items.
Not necessary to replace the left fork leg if not broken.
4) As mentioned, there are several suppliers of complete replacement cartridges from about $600 up to about $1200.
Those will usually replace the internals of both fork legs with adjustable guts. Some are drop in and some require machine work.
5) Replace both fork legs with a pair of Gen 2 fork legs (DO NOT use just one Gen 2 fork leg). They will be a straight swap and give adjustments for compression and rebound in both legs. Occasionally a pair will show up on Ebay at a fair price, lately most have been too high priced. Don't find any right at the moment.
(I currently have a pair of Gen 2 fork legs on my 2014. I like them better than the original 2014 forks)
6) Well dream up your own options or someone else will be along shortly with another option.
As a word of caution to others, again, a fork cartridge holder should be used for disassembly / reassembly instead of an air wrench on the retaining bolt to avoid the obvious damage.
And, the torque specs listed in the FSM are for dry threads. Since it's nearly impossible to have dry threads in an assembly that holds oil, the torque values should be reduced 25% - 35% for lubricated threads.
Good Luck,
dan
YMMV