It's weird that every time I think I'm going to know how to do something, it
winds up I get 1/4 or 1/2 way there and then stuck.

On Sheet1 I have one column of text values (about 500) in Column A (w/
header of "Unique"). On Sheet2 there are many columns and many rows, with
all kinds of values everywhere. What I need to do is:

Run through Sheet2, and for every occurrence of a value in Sheet1's "Unique"
column, enter the column heading(s) of the column(s) that value is in in
Column 2 of Sheet1 next to that value.

For instance, Sheet1's "Unique" column has:

Gear
Tranny
Door

On Sheet2:

- The value "Gear" is located in A5 (Column heading of "Parts"), E114
(Column heading of "Labor"), and G55 (Column heading of "Misc").
- The value "Tranny" is in B45 (Column heading of "Traps")
- The value "Door" is in A88 (Column heading of "Parts") and E6 (Column
heading of "Labor").

So, after I run a sub procedure, Sheet1 should show the following:

Gear Parts,Labor,Misc
Tranny Traps
Door Parts, Labor

I don't care if it's easier to put each column header instance in a separate
column on Sheet1 (instead of values separated by commas), because I can
combine them as a separate step. Also, if getting the actual column header
value is a big complication, I don't mind just returning the column letters
and then I can run a sub or use a formula to change column letters to their
respective header names as a separate step also.

Can anyone help me figure out how to do this?

Any help is greatly appreciated, and thanks for reading.