Are the parts both made of PLA? Silicone caulking would be elastic and easy to break but it might also become unstuck on its own since the adhesion to plastics is not great.
Rubber cement would also work in principle but it might not be reversible at all and depending on the solvent and what plastics you used it might damage the plastic parts while the solvent is drying. Acetone can damage ABS plastics for instance.
Would a low-temp hot melt gun work? They can operate as low as 120°C which might be low enough to not destroy the plastic parts.
Are the parts both made of PLA? Silicone caulking would be elastic and easy to break but it might also become unstuck on its own since the adhesion to plastics is not great.
Rubber cement would also work in principle but it might not be reversible at all and depending on the solvent and what plastics you used it might damage the plastic parts while the solvent is drying. Acetone can damage ABS plastics for instance.
Would a low-temp hot melt gun work? They can operate as low as 120°C which might be low enough to not destroy the plastic parts.