Arm/Tendon Damage

Hello Everybody!
I'm now a 48 yr old male of poor fitness level.
This is mostly due to constant niggly injuries sapping my motivation.

Around ten years ago I injured myself doing reverse grip chin ups. Palms towards my face..
It wasn't an incident of injury but rather what I perceive to be a cumulative effect.

The injury is inside the crook of my elbow in the centre and extends up and down each of my arms by no more than an inch in each direction.
It's best located if you hold one arm out almost straight and place your index finger in to the squishiest (complex medical term) bit right in the centre of the bend.

At its worst I couldn't bend my arm without discomfort and for a month I couldn't pick up light objects without feeling the same, or worse, discomfort.
My biggest irritation is worrying I'll make it worse so stopped all exercise that involved pulling for a few years.
Upon returning to the gym I'd gently test my capability, only to find that the injury recurred. As a result I stopped all exercise for a couple of years and when I returned only really did spinning. (Then I pulled a hamstring... ugh)

I returned to the gym 6 weeks ago and started spinning gently to ease myself back in and then also rowing.
I've worked a zero resistance and worked diligently on good form, starting at 3 mins and building up to two 6 minute work periods with a 2 min break. I'll add a minute per week to one set until I'm more capable. Cadence is reasonable. I'm not hammering it.

I stretch my arms before, between rowing sets, and after the cool down.
I've started to feel the discomfort very lightly once again.

Does anyone know what is wrong?
Must I stop exercise completely?
How can I manage this?
Am I likely to do irreparable damage if I keep going or should I push through?

Thanks in advance.