190 2.6 missing on start

[Jnolee]

The car, a 1989 with 72xxx easy miles, starts fine when cold ( not warmed up ). When warm it often will start with one or more cylinders not firing and will smooth out in 30 to 60 seconds. Sometimes it will not fire on enough cyls. to keep it running and a second or third try is necessary. It has experienced this trait for several years but getting worse. Dealer suspects injector leak down and suggests a new set. If I leave the key on for a few moments for the fuel pump to normalize befor cranking, it makes no difference. Someone have experience with this? I have tried Techron several times to no avail.