
Originally Posted by
Edelweiss
Looking at the manual on Dalong.net I think I know exactly what the cause of this issue is. I suspect you probably had some polycap flash (extraenous moulding material) left on the (let's call them "male" cylindrical portions of PC123 E in the below picture)...
...Also regarding the Action Bases (I don't use them, so i'm not 100% on the following): they may or may not have an "older" kit adaptor (which was basically a glorified crotch area seat in a U-shape form I think), because these are actually a relatively mid-late last decade introduction (the HG Aegis is a 2002 vintage kit, so that's like 5 years prior). I think any of the other regulars here could probably help you more with the particulars of 1/144s, as i'm strictly a Master Grade guy.
Edit: I contacted Tatsu Hobby - TL;DR: Action Base #2s (clear or any color) should have no problems supporting all 1/144 scale Gunpla as long as you use the appropriate-sized included adapter. If you find it's too snug or something, just trim it via knife or cutting shears tool.