DRAM is RAM that fades. It is built from a single transistor and a capacitor and the charge slowly leaks, so you add a refreshing circuit that pumps up the charge again.
Why bother when there are battery backed up RAM chips that hold their state for as long as the battery is is charged or better yest use Flash RAM that doesn't even need a battery ?
Speed. The speed of DRAM especially the write speed is much faster even allowing for the refresh time.
(Also Flash RAM from this vintage has a life of 100,000 or so writes before it may start acting up, so it is not much use for twisting a control and changing the edit buffer of a patch.)
There are essentially two DRAM failure modes. An occasional failure is usually due to radiation. These occasional failures are not at the same locations and are the sort that will cause you to reboot your computer and never to be able to recreate the error.
The second type is repeated failure at a single location. I can't remember the reason.
Unfortunately this is the location on the chip dying. There are some systems that will mark the location as 'bad' and work around it, but I don't think the MP-7 is such a system.
The DRAM is usually on a DIMM board, as in your PC, but on P2k systems it is on the motherboard.
It could be replaced, but needs a tech use to desoldering such complex chips.
As DRAM is fast, it is electrically sensitive and usually needs to be soldered and not socketed.
So either it is an occasional blip or you will need a new motherboard as it becomes unreliable.
Royce