hunting for addslots. any tips?

[K_I_R_E_E_K]

I think the section ID Redria has a slightly better chance of finding red items in general but that's it

Redria can't find half the red weapons and in some cases the drop rate is exactly the same as other ids.

My friend has this theory that the higher level your character is, the better chances you have of getting rare drops on lower levels

Nope, drop rate remains the same no matter the lvl.