T-tray stay looks quite thick. Shock absorber in there?
Also, an guesses as to what those black streaks are on the plank? They seem to begin uniformly where two of the plank boards meet.
Edit- The streaks on the rear section of the plank may be from track use. The front section is clean because it has been replaced. The rear section probably rarely if ever contacts the track so it might get replaced less often.
Edit- The T-tray stay appears to be a sleeved. A sliding joint within is my guess. Some sort of shock absorber for riding on the plank. Zoomed image: