Fuel cap spring 72 bay

I'm trying to replace my fuel cap spring as it wasn't closing. I managed to take the old one of quite quickly with no problems at all. Problem is I can't get the replacement one back on. Is there a knack to this?

 

Take the flap of the van. You need to move it/hinge further than is possible with the flap fitted.

 

Typically, I got it in on the next try.

 

Oh, I just managed to get it in by pushing with a screw driver. It popped in. been trying for 1/2 before posting.

 

Do you find the new spring works ok? The paint shop lost mine when it was there and the replacement has been a bit rubbish!

 

It's possible to fit them back to front and that does make them rubbish.