I hardly ever clean my rifles so it hasn't had any cleaning done

I sight all my guns in at 100 yards. Everything from 22 mag to .308. It could be the scope rings . My .22 mag had a problem very similar to that changed them and now shoots great.

Had the same scope rings and base since 72 on it up until this year. Scope was needing updated so that's the only thing that changed. So I believe it's a scope issue but want to be sure.

Just try different scope rings. With my savage it was shooting everywhere put different scope rings on it drives tacks now.

Well everyone ought to use what works best for them. If a buck with a small rack is okay and you are in brush country with a lot of twigs, even 70 yards can be sort of hard to make out a rack. You should not "glass" an area with a scope sight but if you see the deer then a scope is a fast way to tell if the deer is wearing antlers. I used a 4x but it was a little too small a field of view. Bushnell had a 2 1/2x Pronghorn (not sure if they still make it)- fixed power. I've tried a couple of variable low priced scopes that were junk- would not stay on target- kept moving around. If you have a cheap variable scope- that could be it.
To bore sight on a Marlin, remove the lever, depress the hammer, and just pull off the bolt. I use a cardboard box with V cuts to hold the rifle. When the bull is in the center of the bore I look through the crosshairs and adjust. Usually the first shots are only 3-4 inches off- very easy way to sight in a scope.

Someone stated that they loctite pretty much everything. I believe in only loctiting the base screws. Fingernail polish works well too if you don't have loctite.

I mount scopes daily at work and also do it on the side. If you have had the bases and rings since 1972 then they are probably steel and I doubt they are the issue, though they could be. My first guess would be that it is the scope. The easiest way to tell where the issue lies is to mount another scope on your rifle and see what happens. I understand that isn't always possible. Don't recall you mentioning what make and model of scope you have. If it is a bubble pack scope then I would bet on the scope being the culprit.

It's a weaver scope don't recall model but lower end

I've got pics of the front mount but can't get them to upload. Not sure how to go about doing peep sights with the front sight I have now.

Looks like that front sight hood is mashed down. The bottom rail on the hood should rest in the groove not the bottom of the front sight mount.

On the peep, that's what I used when I was younger. The choice of sight depends on what best suits you. Weaver usually makes a good scope but as I said I just have not had very good luck with the variable 3x-9x types. There are more parts to shake loose and the fixed just seem better. On a variable- if that's what you have- you often need to spend some money.
I'd test the scope on another rifle.

Ordered a set of peep sights so I'll give those a shot

It was going to be my go to this year but it may be a backup but east Texas hunting a lot of times you don't have time to get in a scope and ready.

Ok for the peep sight guys. Install is pretty simple. But do I need to install both screws in the rear sight? Came with 2 different size screws and only one size fits.