If it's a D400 mkii, I bought one off Ebay and the caps were leaking. Tons of feedback. I sent it to Pyramid Audio in Austin. AR won't touch those anymore (as previously stated). I think the old caps are Philips, but don't quote me on that.
When I spoke to the tech, he mentioned he was warned off even trying to repair it (by other techs) on forums and FB groups.
Luckily, he tried and found some that worked (don't know what they were). They needed to be direct-soldered. This was about a year ago. Give Pyramid a call and see what they say. My amp sounds great now.