What Kelson said sounds most likely.
The DVD burner can fail in a couple ways from age, and it doesn't require continuous use to fail.
The central hub is made of rubber, to grip the central spindle of the DVD and give it torque to spin. Over time that rubber is subject to attack by the environment from things like ozone, and microbes that like to eat the latex in the rubber and turn it to slippery goo.
Once the rubber degrades you can't really stabilize it again.. you can try to rub it off, clean it off with alcohol.. but it was there to "grip" the disc if its rubbed off it won't be there to grip the disk and will slip even worse.
If the drive is not "too" old cleaning the rubber hub can "kind of work" for a while.. different people try different cleaning fluids.. including spit.
Don't leave a DVD in the drive for a long period of time (like years) the goo can turn to "glue" and then the drive will not open or release its grip on the DVD.. they will have bonded.. in a messy way.
The more common way to die is for one or both lasers for CD and DVD media to die.. and you can't really replace those. Magnavox / Funai no longer sells replacement DVD burners for any of the DVD recorders that it used to sell. They stopped selling those replacement parts in 2017.
Finally there is a tiny rubber belt, which drives the loading mechanism which (because its made of rubber .. aka latex) can stretch and slowly turn to goo itself from attack. Sometime you can get at this belt and replace it.. some people swap the o-ring shapepd belt out.. some take the old one out and semi-boil it to clean and shrink it back into shape.. (see youtube videos).
But eventually the DVD burner is going to fail.. they don't last forever. For that matter the hard drive and the power supply will eventually fail.
The Mag 515 has a pretty good used resale value on eBay.. I believe it has an ATSC tuner which means if people can find the parts or use the parts from yours.. they can fix one and keep going.
Another option is you can take the hard drive out and copy recordings off by connecting it to a PC and using Isobuster Pro 4.4 This is a piece of software which gained the ability to recover recordings from DVD recorders like the Mag 515 this year (2019). Its original intent was to help recover personal videos from camcorder footage or wedding and graduations that were marooned on a DVD recorder with no way off the Island.. but it doesn't discriminate between recording types.. it can help you recover any recordings from the DVD recorder hard drive to a PC and then you can edit and burn them to the PC DVD burner.