Ricoh 5510L replaced toner and still getting black markings on page.

Good day everyone.

I've been working on a RICOH 5510L for the last month and have run into a consistent problem. After purchasing the beast I noticed it would always have black lines across the page. So I cleaned / replaced rollers and obtained a new toner cartridge. (The fuser was also replaced unable to heat up in time)

Attempting to solve the problem has failed, the new toner is darkening 2/3 of the page and fading all text. I've thought about getting another drum to see if it's just a faulty rebuilt cartridge but cost is brutal.

It's hard to find much discussion on this particular model and the booklet has run me around in circles, any help would be very appreciated.