Burghley Park Golf Club member Eric McKaig, 70, of Fane Close, Stamford, has ignored medical advice and joined a growing number of people who use the lubricant to ease their creaking, painful joints.
And he swears it has ended his days of pain and given him his quality of life back.
The retired sales manager, who used to play centre forward for Nottingham Forest in the 1950s, said: "It's been an absolute Godsend for me. A few weeks ago I was even running around the garden with my grandchildren and I haven't been able to do that for about three years."
But the manufacturers of WD-40 are urging people not to follow suit.
The company said: "The spray has thousands of uses, but treating stiff joints is definitely not one of them. The product has not been designed for use on the human body and has not been medically tested. If
you are suffering from joint pain you should always seek advice from your GP."
Mr McKaig began getting stiff and sore joints about seven years ago and visited an orthopaedic surgeon. X-rays showed his knees were crumbling. And he claims he was told that no action would be taken until he was unable to walk around the golf course.
Mr McKaig, who plays off a nine handicap, said: "I am a golf maniac and play every day when I can. I had a long hard think about what I could do. I tried painkillers and supplements, but they didn't really work. Then I thought about a friend of mine, Ron Andrew, who had been through the same."
After nearly 10 weeks of nagging and gentle persuasion Mr Andrew, 78, of Ketton, finally shared his secret with his friend. And his secret was WD-40.
So Mr McKaig took the plunge and sprayed it on both knees before massaging it in.
He repeated the process again two days later and hasn't touched a drop since.
He said: "Before that I was using strap-on knee braces with magnets on, but this has given me my quality of life back.
"The can quite clearly says that if it comes into contact with skin you should wash it off immediately, but it has had no adverse effects on me."
His partner, Isobel Reading, said: "He was having a job to walk around the golf course, but the effects have been amazing. It is not a cure, it is a prevention, but it appears to be working, so who cares?"