NSX starting problem
 

I own a 1991 NSX with 145,000 miles. Over a year ago, I started having starting problems. The engine would turn over but wouldn't start. This occured after driving the car for at least 20 minutes and only happened 1 out of 10 times. The Acura dealer couldn't find the problem , but wanted to replace the starter. We had to get the new starter from Japan and with labor at a cost of $1300. With the new starter the problem went away. The part is now out of warranty and the non starting problem has resurfaced. Anyone have an idea or similar problem that can be solved another way?