Glues
Acetone is a good solvent for ABS an styrene. Widely available in most nail polish removers (look for 100% acetone), it is inexpensive. Can be applied with a paint brush, but evaporates fast. It has a very thin viscosity so it can be applied from a thin syringe.
Lew
Florida ⛱️, USA ❤️
Update:
I find using the regular Testors or Tamiya solvent cements work well, both the bottled liquid which is slightly thicker tan Acetone, and the tube (thicker consistency) work best for me. I do a lot of 3D printing in ABS.
https://www.RCFlorida.org/lmb