Its an old car, they will have simply lost pressure. Buy some new ones, factors sell them, not worth bothering with struts from scrappies, they could well be just as bad.

Must have been one of the very last Escorts made.

Gas struts usually show their weaknesses and fail when the weather gets colder, if the car is fitted with two its very unlikely that just one will hold the bootlid up.

Easy peasy to fit, but worth shopping about for prices.

www.sgs-engineering.com/gas-struts?gclid=CPPujZ7Wg...w

I used to engineer gas spring installations for Rover and Land Rover - I'd advise against regassing services.

Likely to be partly the drop in temperature. At ten years old these things can get tired, but they don't all fail at the same rate. Should be possible to find a scrap car with them still in place so you can test.