Itinerant Air-Cooled

Quick question for the experts.
I just changed the oil in my 82 aircooled westy, and at the same time, I checked the oil pressure relief valve and spring. The piston moved freely, and looked fine. I also bought a new spring for it, but when I compared the new one to the old one, the new one was about 2-3 mm longer. I've never changed the spring in the past 24 years, so I guess it could be normal wear on it? Or are there different springs for the late air cooled motors?
The one I got was from bus-depot, and they show that it is the same for the late 70's bus up to the 83.5 vanagon (and the water boxers too).
Thanks!

there are specs for the spring and length in Bentley. You can use a bathroom scale and a dowel cut that length to approximate the compressed length. Cut a wooden dowel to the compressed length in Bentley and put it inside the spring. Compress the spring on a bathroom or postal scale etc - the pounds will go up slowly as you compress it until you hit the dowel and then you will see the pounds jump quickly. You will also feel / see the dowel touch whatever you are pushing down with.