When my car was bought by the original owner in 1991 Ford had what they call lifetime warranty. So when the original owner paid for some parts to be replaced in 1993 (lifetime warranty on parts ended in 1994 i think) the parts that were replaced came with a lifetime warranty (basically their warranty stated that all parts replaced should last forever unless mistreated).
For me this was front and rear shox, thermostat, power steering hose, power steering pump, radiator cap and a couple of others. Ford ended this warranty idea in 94 because they were losing too much money, too quickly. But all parts that were replace by ford before 1994 (with a reciept of course) should be covered under lifetime warranty. You can usually tell because next to the part name on the reciept there is usually an asterix if the part has lifetime.
On a different note the grinding isnt anywhere near as noticeable at high speeds.
No continual services (by ford or anyone for that matter) aren't requied to still recieve lifetime on all parts covered