How much rust on trailing arms before replacing ?

[Green Machine]

Pulled the rear end and arms from my 70 C10 as an assembly. Was just going to clean and paint, Passenger side arm looks great, but driver side is spread at the middle. Used large hammer to knock out some of the rust, now there is a dime size hole on each side about 12 inch in front of spring, tops and bottoms look solid, I think its still strong enough to use, but would you replace or just run it for now and consider keeping and eye on it if it gets worse ? Thanks