There is a detail that you have missed in that clip where treadwell extends his welding arm to repair the moisture vaporater. This is animation based effect where the extended arm is paused to composite the welding effect on the droids arm.
I actually plan to back later and work more on that clip. I will need to see that missing part is, I did not think I left out any scene
It’s there where Luke runs off screen past treadwell to the landspeeder. Treadwell droid lifts and drops his arm.
You need to pause the frame of the video where his arm is fully extended then composite sparks on the still image once he is done repairs continue the video and his arm drops back down. Magic.