I replaced my GP's last year, the original ones, as ill conceived preventative maintenance. In fact, I got hollered at by PE Haiges for doing so.

I had two go bad in the last year,,, all Bosch.

If it ain't broke don't fix it,,,,, but if you can't help yourself, take your time and use plenty of the penetrating oil recommendations.

Final note, my 300D is a 1977 and the original plugs worked just fine. I wish they were still in my car.