The Moon and the Great Wall

Question

_{This puzzle is part of the Monthly Topic Challenge #1: Restricted Title: xkcd 1xxx}

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Instructions for this modified connecting wall:

1. In the connecting wall below, each item as written contains one letter too many. Once this spare letter is removed, the real word to be categorised is an anagram of the remaining letters.
2. Appropriately categorise these anagrams into four groups of four, as per your standard connecting wall. The themes for each category are... well, you'll work it out soon enough... The four spare letters for each group can then be anagrammed into a real four-letter word. (In some cases, more than one anagram is possible - you will need to deduce the intended one when working through Step 3 below...)
3. These four four-letter words are in turn linked by one final (contextually appropriate) five-letter word - what is it?

ABORTION	CHIANG MAI	DURIANS	ESPECIAL
FEDERAL	IN THE CLEAR	MALISM	MOULDED
OH DEAR	OINKED	ONRUSH	PETUNIAS
PRETORIUS	SERAPH	SYNDICATE	TITIAN

Answer 1

This is truly the Moon and the Great Wall!

The groups are

Moons of Saturn:
malism -l = MIMAS
titian -i = TITAN
oinked -k = DIONE
petunias -n = IAPETUS

Great Lakes of North America
onrush -s = HURON
chiang mai -a = MICHIGAN
pretorius -t = SUPERIOR
abortion -b = ONTARIO

Monarchs known as the Great
in the clear -l = CATHERINE
durians -n = DARIUS
oh dear -a = HEROD
federal -e = ALFRED

Words associated with Lunar
especial -a = ECLIPSE
syndicate -y = DISTANCE
moulded -d = MODULE
seraph -r = PHASE

This gives the four four-letter words

KILN, BATS, LANE and YARD
which are linked by the word
BRICK
as is, of course, also the final word of the title, WALL.

Answer 2

Partial answer, will have to revisit this later when I have more time.

The first group:

ABORTION = ONTARIO + B
CHIANG MAI = MICHIGAN + A
ONRUSH = HURON + S
PRETORIUS = SUPERIOR + T

These are four of the Great Lakes in the US. The four additional letters anagram to STAB, BATS, TABS...?

The second group:

MALISM = MIMAS + L
OINKED = DIONE + K
PETUNIAS = IAPETUS + N
TITAN = TITAN + I

These are four moons of Saturn. The four additional letters anagram to LINK or KILN.

The third group:

DURIANS = DARIUS + N
FEDERAL = ALFRED + E
IN THE CLEAR = CATHERINE + L
OH DEAR = HEROD + A

These are four historical leaders who had "the Great" as their title. The four additional letters anagram to LANE or LEAN.

The remaining words:

ESPECIAL = ECLIPSE + A?
MOULDED = MODULE + D?
SERAPH = SHAPE + R?
SYNDICATE = DISTANCE + Y?

Unsure about this group. I originally had SHAPE and DISTANCE as two of the solutions because I thought DARIUS might be RADIUS and they were all geometry terms or something. So it's possible some or all of these are wrong, there are certainly other anagrams possible.