I was thinking that I might be the only other person in Canada with a Lakefield Mossberg Mk1 single shot, since I have never seen another. Mine has peep sights on it because it was purchased specifically for me to use as a target rifle at an indoor range. When I was given mine 35 years ago it had an ejection problem and my father and I took it back to the shop where he bought it for me. The shop owner - now since passed away - was a legendary gunsmith and he fixed the problem in minutes. My advice to you is to take it to a gunsmith and have it worked on.
I still have that rifle and it looks nearly as good today as it did the day I brought it home for the first time. My late father gave it to me, so it won't be sold... ever.