How do I go about fixing this strange dark line blocking my Minolta XG-1's viewfinder?

Question

I recently bought my friend's Minolta XG-1 which looks super well maintained cosmetically. He did mention to me that it was sitting in his hot attic for about a year.

I noticed that there is a weird black line covering about 25% of the viewfinder. It has a weird bubbly texture and I suspect it has to do with something on the prism itself. I tried cleaning and thoroughly inspecting the mirror and the focusing screen (I am new to photography so I am not sure but I think that's what the thing above the mirror is called) and found nothing suspicious. There is barely a single speck of dust left after cleaning everything.

Additionally, the weird line in the viewfinder is still present if I look through it without a lens attached.

What steps could I take to attempt to clean this out?

This is a picture of what I see through the viewfinder:

Answer 1

Age and heat have detrimental effects on any lubrication or seals in a camera. Heat may have caused the the substance that hold the prism in place to soften allowing the substance or the prism to shift.

The shutter and film winding mechanisms also need proper lubrication in order to function as designed.

The best coarse of action on any old camera is to take it to qualified camera repair shop and get a CLA (CLEAN LUBRICATE ADJUST) service done on it. Especially since you know it was stored in a hot space and it is OLD.

Minolta XG-1 online manual.

What is CLA service?

Repairing and Maintaining Classic Cameras

Answer 2

I know that this is now from two years ago, but after some careful digging through a camera that was totaled and had the same issue, I have found some unfortunate findings on this matter. This issue is caused by an adhesive strip degrading the mirror coating on the viewfinder prism as seen below. I am currently investigating a solution but taking this issue to a camera shop for a clean, Lubricate, and Adjust will not solve the issue. This is a degradation to an integral part of the prism.

Answer 3

The online auction site value of an XG- 1 appears low enough that replacement with a fully functioning camera identical or similar model will be less cost than the cost of professional repair.

At the time of writing KEH has a working XG-1 for about 30USD with their 180 warranty.

Selling the defective camera for parts could offset some of the replacement cost.

While you can try repairing it yourself it is probably a bit over complex for a first project unless you have substantial relevant experience.