Valve seats failing ! 1.9

Any body have any data on why these 91 to 96 1.9 motors drop valve seats? I have 5 Escorts & 3 out of 5 had valve seats fail in the last year ! Two 95s & one 94. They have been service & never over heated.One chewed up the cylinder wall that bad, that i had to put another motor in it. The others just took a heads. Im loosing my faith in them!!

How many miles on them, what octane gasoline do you use? Anything over a hundred thousand miles on 87 octane is doing good, either switch to 91 or have the heads rebuilt.