Problem replacing a disk in a PowerEdge T710 RAID 1 on LSI SAS 2308 controller

This problem is occurring on a Dell Precision T7610 with an LSI SAS2308 RAID adapter.

The computer was delivered new with two 512GB SSDs configured for RAID 1, forming the boot volume. It became apparent that Windows had been badly installed, so after some months of random BSODs, a ground-up rebuild was done. Before doing that, I pulled one of the SSDs, which I'll call D2, so that if the reinstallation went badly, I had that to fall back on. The Windows reinstallation was successful onto D1, but I didn't get round to reinserting the D2 for some time, despite a reminder every time I rebooted that the RAID status was Degraded.

Yesterday, I put D2 back in and rebooted, and was informed that there was no boot device. When I removed D2 and rebooted, much to my relief, D1 became accessible again so the machine started and booted into Windows.

In the LSI config 'Manage Volume' section, with only D1 inserted, it's identified as Slot 0, LITEONIT LCT-512, RAID Disk, not a Hot Spare, and Primary status. The second disk is shown as Missing.

When I insert D2, a number of changes occur in about 30 seconds or so.

• D1's status changes to Inactive, and the second disk's status is shown as Missing.
• D1's Slot changes to 363, LITEONIT LCT-512, RAID Disk, not a Hot Spare, and Inactive status
• D2 appears, also Slot 363,  LITEONIT LCT-512, RAID Disk, not a Hot Spare, and Inactive status: in other words, identical to D1.
• Both disks then disappear from Manage Volume, leaving it empty.

As I'm not familiar with this RAID controller, I'm rather wary of it. Unsurprisingly, what I specifically want to avoid is losing D1 or getting it into an unusable state. Although I have a full backup, I really don't want to go there. From reading the controller's documentation, I think one tactic might be to try to reconfigure D2 as a hot spare and then bring it back into the array with D1. That might be easier said than done, given that it appears with what I'm assuming is a spurious slot number before disappearing completely. As both disks are listed with precisely the same information, I've no way of telling exactly which is which. I have no reason to think that D2, which sat in a box for a year or so,has failed.

Can anybody suggest a method by which I can get D2 back into this controller's array without endangering D1? 

Thanks in advance for any knowledge you can share.