Hello from Canberra, Australia - just discovered and signed up to this forum after looking for a solution to a cracked subframe on my 2010 FJR.
This is a great resource, keep up the great work!
Rogor, like Russ said this is a really old thread that probably won’t get much attention for your problem but i’ll Give you my input on it since I also broke the rear subframe on my 2014 (very poor design imho) and these are your options.
1) Buy a new one ! Cost on partzilla is about $600 all in, and install it yourself which is not hard but quite involved and time consuming, all told if I remember right (questionable) it took me about a week to change it out. But very do-able.
2) take it out and tig weld it back together, add some reinforcements to improve the structural integrity of the rear “tab” to keep it from flexing which is what breaks the lower part of the subframe.
3) no matter which option you choose above once it’s fixed add a givi sr357 rack, a Shad tube rack or a new heavy aluminum Yamaha rear rack to replace the current cheap plastic rack. You need to do one of these to keep from rebreaking the new/repaired subframe. I am assuming that you are running some kind of top box which is what caused the frame to break.
I added the Yamaha heavy aluminum rack myself in addition to heavily modifiying my “ stiffy” bracket o keep the rear tab from flexing along with some additions to help support the lower portion of the frame and keep it from flexing as well. That’s what I did, good luck !