This is like a mission to a mission for a mission xD. I shall try that later, thanks.Had that exact issue today, here is what I did to solve/bypass the issue since the booster piece didn't spawn no matter how many times I loaded to before even getting close to the Mine Island. Give it a try, so you don't get stuck there while the devs try to fix/patch it. Here are the steps:
1) Go to the mission area. Destroy Gruntle, collect his pieces if you want. You will not see any more dialog, but the mission says to "Fix wimpy" (bug).
2) Go far away from the area (turn into a mini-plane if you have one) and make a fresh save (a new one, don't overwrite your past saves specially if its before ariving to mine island).
3) Close the game completely, then open it up again from steam.
4) Load back the game from the save we made, being far away from the area
5) Return to Mine Island (if the mission is still active just follow the misssion marker again) and now there should be a Little Stud Pulse Booster near Wimpy and he should now have dialog telling you about helping him be repaired, when you pick up the booster one of his arms will have a yellow aura telling you where to attach that part, do it exactly there. If you put it elsewhere it might bug the mission and make it unobtainable (since you cannot take parts from him, if that happens don't save and load your past savefile)
6) After you receive your chest reward take a deep breath and save, phew!