Pin bushing housing.. what is it?

[keynote22]

My c43 transmission is leaking. The shop says its the pin bushing housing and wants $300. What it this, where is it, and how bad are they sticking it to me? They just did a tranny fluid swap.. is that something that should have been corrected during the swap? It didnt leak prior to the tranny fluid swap.

The quote says parts $5.75????? the rest is labor and fluid!