Here is an easy trick to make welding seams perfectly alike and realistic texture. We will need rests of the models plastic panels, nitro solvent ( universal solvent, in every paint shop ) and some cotton thread.
We put some solvent and some plastic bars in a cristal bottle and wait them to melt.
Then we moisten the cotton thread in thi sliquid plastic and we apply it to the model.
Once dry the cotton thread has absorved part of the plastic so it can be sanded and painted as any other part of the model.