I'm sorry but I wasn't able to find out anything encouraging.

The man at the sheepskin store where we shop said if required wash in cold water with a gentle eucalyptus woolwash. They should last 20-25 years. As you don't need to wash it, just restore it, you could try pure lanolin or glycerin but he'd never heard of that being very successful. Pure lanolin (not lanolin-containing creams) is apparently available in chemists/pharmacies.

The man at the sheepskin and wool store said they should last 15-20 years, didn't recommend washing and thought you'd have to send them to a tannery for restoration.

The man at the local tannery said he wouldn't attempt to restore a 40 year old sheepskin. It would be useful to know how they were tanned because some shouldn't be washed.

I tried google.com.au which just repeated the advice to wash in cold/warm water with a gentle woolwash. One website listed things to avoid - enzymes, phosphates, peroxide, alkali, bleach, triethanolamine and sequestering agents. So that got fairly technical, but still no info on how to restore. Oh, and avoid heat and sunlight.

I'm now thinking maybe a textile conservator at a museum might be able to suggest something. The only thing is they preserve things for display, not for use, so that may not be so helpful after all.

Thank you so very much! Excellent information! First, I did not know a 'livespan' for sheepskins. Sounds like we have more than already gotten our money's worth from them. Never thought about 'pure lanolin' and will buy to experiment for sheepskins and other products lanolin may benifit. I may try washing a corner to see what happens and if the wool doesn't curl like crazy a bath might be an option. I was shocked how much dirt I combed out and how black my hands got. I guess, even not appearing soiled, dirt/dust clings to the lanolin and can't shake or vac out. If unwashable, I think I will make machine washable covers and we can use them in our cars, seat covers, beach pads, etc.
For anyone else attempting this, I learned to do this outside on a nice day. Can't believe what a mess I made inside and it 'floated all over the house! Never do that again! Alot of wool combed out but I'm recycling, letting the birds have it all for nesting material.
Again,Mac, thank you for helping me. You are great!