Your sprint boat looks good. I like the roll bars alot. I also tore up the u-joint that came with the mini jet drive unit. I switched to a metal ujoint for the shockwave 26 or the apache 24. The only problem was you had to ream one side out to 1/8" because both sides are 3mm. But the best replacement I found was making one from the larger graupner ujoints . I think you can get the 4mm X 3.2mm one. It is larger than the 3.2 X 3mm one so you have to make a motor mount and move the motor a little forward. I run mine with 3500kv heli outrunner and it works great. Vibration went to null. I think hobby lobby has them. It comes with a middle part (don't use it) and an brass insert for the 4mm side to make it fit 3mm. The other option is to use a flex coupling also made by graupner. They also work well but move the motor much farther forward. You would also have to make brass insert adapter out or 1/8" brass tubing. Or do what headhunter said. That would help straighten the shaft alignment for sure. below are pics of both examples I gave you.