I ordered a set of 2DW232 from AliExpress, and they were delivered last week (no time for measurements, yet).
They ended up being "15-4" date code with a painted red dot on each. Inside, they have the smaller die (barely larger than two bond pads), covered in the white RTV-silicone-like substance.
The wire-bonds are not gold. I left a 2DW232 in salt water for the day, and the wirebond is still intact. I'll assume they are silver (which has a reasonably low thermal voltage with respect to copper and gold).
Why is the silicone used? One total guess is that it is to block the emitted light (mentioned earlier in this thread, I've not looked for it) in order to reduce the coupling between diodes?
Also, an interposer layer would be a good idea in order to reduce mechanical stress, though this would likely require a third bond pad and a more complicated silicon process to maybe do an extra implant for a top-side contact.
The leads are magnetic, and don't seem to easily rust, so I'll assume they are kovar.