I've owned 12 C10's and have had two with hydrolocked bent rods. Granted I am the guy picking up the non-running ZG1000's when I can find them, so the odds of me getting one is higher than normal.
Since I was buying them for parts bikes and at the right price, I didn't care. (1 was free!)
The first was so severe the engine would not rotate the full 360 degrees. The first 2 pics are of that rod.
The 2nd had a knock where the rod was hitting the balancer shaft on each rotation. It is shown in the last 2 pics.
The fuel in the engine can be dealt with, but most importantly you want to do a piston height measurement on the 2 pairs (1-4 and 2-3) of pistons.
You don't even need to turn it over but its nice to have either pair closer to the top when measuring.
Easy to do with a wooden dowel and a tight piece of tubing to set the depth on each, then measure with a ruler to compare.
The pairs should measure identical. If not, there is a bent rod in there that is often not discernable when hearing the engine run.
Then it all depends on the price and your ultimate intentions for the bike.