External Thermostat repair question 87 Carrera

[VMAX1]

I got lucky and all 4 broke loose and I got in removed, after 2 evenings and a pint of knuckle blood. Since its off the car, should I replace the parts inside the bottom plug? Looks like all I can get is a pressure spring, cap and seal for the cap. The piston is NLA. I do have a new piston, cap and cap seal for the side. Next question, good and snug going back on with the nuts? Cause they were hanging on for Life trying to get loose. Thanks for the help.