Carambola - bark disease?

[IndigoEmu]

I first noticed a small amount of bark splitting on my Kari carambola about 6 months ago. I trimmed the tree a bit and noticed that it’s progressed a fair amount since then. The afflicted trunk areas do not have a full, rounded circumference. It’s been in the ground almost 2 years, but I find it’s vigor has been lacking. I haven’t fertilized it much so that may have played a role. I let it hold around 20 fruit this year but almost all of these dropped before ripening sufficiently, and the taste of those that did was severely lacking. I haven’t been able to find much information on diseases that affect carambola trunks/bark. What’s my best course of action? Trash the tree? Cut off most the diseased growth? (which would mean stumping it’s just above the graft...but I do see some slight cracking reaching the graft line) Or simply leave the tree and see how things play out?

[IndigoEmu]

I was thinking about just stumping it’s below where I see any cracking. I’m pretty sure I’ll lose the graft but I could always re-graft myself next season. Never grafted before but I figure it’ll be a chance for me to learn. What method should I use for a 2.5” caliper trunk?