I have a Petri too, handed down by my Dad, with the wide and tele attachments. There are no stronger ones available. These are not expensive cameras, and while the lens on mine is sharp, the cameras filled a lower-quality market niche.
My Petri had some problems with the shutter cocking and film transport; I had it repaired locally for $85, far more than it's worth. He had a lot of difficulty cleaning out old stiffened grease that was gumming up the works, and replaced a weak shutter spring. But probably as with yours, there's some sentimental value, and I like my stuff to work. There are a couple shots in my gallery here taken with this Petri.
You might find some useful info on Petri cameras at Karen Nakamura's Photoethnography website: http://www.photoethnography.com/ClassicCameras/