David C,
By no means do I consider myself a guru after only 3 full years of repair. I will however share some ideas with you on this subject. I did have a question for you first though? When your looking at the break, what criteria led to your suspicions that it might be a runaway?
Heres' one of my suspicions. Using a magnifying glass (great tool to have as mentioned in a previous post), I'll closely inspect the tip of each leg. If I locate any tips that are rounded or come to a dull point instead of a sharp point, I'll always exercise extra caution! For some reason I've found these guys always want to travel somewhere! Once I find these, I'll then mark the tip with a paint pencil, take my probe and carefully apply pressure to these before even attempting to set up my equipment. If they grow even a micro in length I know it's a fragile repair that's requires both patience and baby sitting. Sometimes I find myself leaving a small tip at the end of these legs, knowing that what I've already filled will bond and keep them from expanding. I'll also explain to the customer that if I forced the issue with these open tips the leg could possibly run. So far nobody has ever complained. Unfortunately, I've had a few bad experiences when the leg did start to run. Only then did I have to drill a block to stop its progress. Once again, I'll explain in some detail to the customer about what happened. If their not happy with the results the repair is always free.
I think one of the common understandings in repair is anything within 3 inches of edge is considered a fragile repair. Whenever I see these, I automatically bring the customer out and explain in some detail why it's a sensitive repair. Personally, even though I have a 98% success rate with these repairs I continue to tell the customer there's a 50-50 chance it may run. Just in case it falls under that 2% failure! I'd rather under sale these repairs then over sale them. Customers can be very forgiving if your open and honest with them from the start. Also takes alot of pressure off me during the repair when I'm holding my breath
I'd be interested what others have to say from their experiences.