It is a DIY, and many of us have done it.

Have a look here:

http://webspace.webring.com/people/mo/ozbrick/door-stay_fix.html

Hope you can see the images. Right now, I am getting the evil red crosses in lieu of the images. Hope your browser is more kind to you.

A word of caution. You must remove the very heavy door, so ask one or two sturdy friends to assist, especially when placing the door back on the hinge pins. Precise location control is critical in order to prevent paint damage. I had one friend help, and I still scratched some paintwork.