$4,000 (to fix ) chasis, suspension, shock problems, with all these Lincolns. Can anyone comment how to know when it is permanently fixed ?

there is no such thing as permanently fixed. They have had this air ride suspension which I am assuming that's what you are referring too since 1984. It all has operated on the same principle with some different setups depending on the model Lincoln you have. You got two options, 1 to have it converted if you are looking for a permanent fix that would be it to convert to typical traditional springs and struts. The other option if its a very nice well kept Lincoln and you want it to be original just repair or replace the parts and components as they break.