Suspect some are worse than others. My 6320 Is certainly better than my 6210 wasAre the 6430s prone to have a fast start on the PTO, I have a neighbor with a newholland and has gone through 2 spline shafts on a baler because of it, Shouldn't all tractors have a soft start?
Surely a small accumulator in that line would be the best bet.If he got keen.. and had a few ideas. He could fit an extension hose off the pto modulation valve pressure port and that would probably make the start a little slower. As to how long the hose would need to be that would be a shed experiment.