I've never used one of those MPD32's but I know they are/were, very popular MIDI controllers for beatmakers. I remember there was years it was always either one of them, Maschine or Push you would see DAW based beatmakers using.
How long have you had it? I know it came out about 10 years ago though so is probably just at the natural end of it's life. There is a never version which was released around 2016, the MPD232, if you want get something new but keep it very familiar. You can pick them up on eBay for under £100 second hand these days. I know they are built like tanks.
Re the SP-404, they seem to be more popular than ever in the likes of lo-fi hip-hop circles, but bear in mind that the pads aren't velocity sensitive, and overall it's not really suitable as a DAW MIDI controller so wouldn't be a replacement for your outgoing MPD32. Unless you want to get out of the box and into the SP-404 workflow, or use it as an FX unit, then i'd look elsewhere.
What DAW do you use? Once I know that I can give some suggestions.
