Is Germany virtually guaranteed the odds G3 on sealion?

You forgot the 5 British AAA, which reduce your chances to 1.5%.
Are you sure? According to the 2nd edition rules, you don’t roll more AAA dice than the number of aircraft. page 29.
Yes, but they can be used as cannon fodder before the infantry die. And since they’re likely to kill 12 planes, Germany’s hit points are suddenly lower than the UK’s.

Germany buys 1 AC and all transports (total of 12).
12 transports on G3. All that economy (11 transports purchased) over two turns almost guarantees a successful sea lion. And it almost guarantees you will lose the war. Sure you’ll get all that money from the UK, but it cost you 88 IPCs to do it.
I am just a newbie but I don’t think you are asking the right question. The question you should be asking is this: what is the minimum amount of Germany transport navy purchased that is needed to get a 51% success rate of sea lion on G3? That is the question. I think spending 88 IPCs on helpless US bomber targets as the Soviets roll over your entirely depleted Eastern front, isn’t worth taking the UK out for two turns.
According to my calculations, Germany can just barely pull off a G2 Sealion, which would be more ideal.
Ger starts with 5 ftrs and 5 tac bombers and 2 bombers. Assuming Ger only loses 2 ftrs and the rest subs on G1, they will be in a good position on G2.
G1 purchase: 4 trn (28 IPC’s).
When taking out the Royal Navy, they may scramble fighters. But this isn’t so bad, because the fighters may then be lost in the naval battle. If UK scrambles fighters, then lose ftr for ftr. Then there will be less defending London. Save the battleship!
Use subs in sz 117 and sz 118 to take out the Canadian des and trn so UK can’t reinforce with Canadian troops.
Place all 4 trn with 1 trn that you start with in sz 113 with the cru and battleship you start with. You need the battleship there to protect the trn from the UK bmb. Position troops and tanks to load onto trns next turn.
UK1: UK builds 9 inf, moves ftr from Gibraltar to London, moves Scotland units to London.
If UK blocks the Ger navy with the cru from sz 91, take it out with Italian ftrs and bmb.
Thus, on G2, attack!
UK should have in London (if they didn’t scramble ftrs)
15 inf, 1 mech inf
1 bmb
5 ftrs
for a total defense of 53Ger should be attacking with (if they only lost 1 ftr to AAA)
5 inf
5 tanks
2 ftrs
5 tac bombers
2 bmb
for a total attack of 54
plus Ger gets a cru and battleship bombardment.Thus Ger should barely win a G2 Sealion.
you should really use a battlesim. You are forgetting the value of hitpoints.
If we forget about the AAs then the germans have a total of 19 units, while the british have 22 units.The number of units you have is much more important than the number of battledice you have.
Running the battle on a battle sim gives germnay about 2% (13%) chance of winning.
adding the AAs as well, and the picture is even grimmer. between 0.2 and 1.6 % of winning.
One thing that might suprise you is the value of volume. If you have 12 ftrs defending a terr and I attack with only infs. I only need about 24 infs to have a 50% odds of killing all of the fighters. To see why the 21 ratio is correct, we can do an easy calculation.
round 1.
the fighters have 124/6 hits = 8 hits on the infs.
The infs have 241/6 hits = 4 hits on the fighters.
that means that the fighters lost 4/12 = 1/3 figters.
the infs lost 8/28 = 1/3 infs.
Which means that both sides lost and equal percentage of their fightingpower.The actual formula for thse kinds of battles where pure infs attacks a pure force is:
inf vs inf sqrt(1) to Sqrt(2) > 1,41 infs attacking per inf defending
Inf v tanks : Sqrt(1) to sqrt(3) –> 1.7 infs attacking per tank defending.In axis volume is king.

I suppose the best way to do Sealion is if it’s a surprise. i.e. buy 2 bombers and 2 inf on G1 and move land units east to make it look like you’re going after Russia, so the UK player spends their first round money on sea units, then on G2 spend all your France loot on transports and attack London in G3.
Of course, the second time you do this your opponent will see it and build 9 inf in London on UK1. But then you just go after Russia!

I suppose the best way to do Sealion is if it’s a surprise. i.e. buy 2 bombers and 2 inf on G1 and move land units east to make it look like you’re going after Russia, so the UK player spends their first round money on sea units, then on G2 spend all your France loot on transports and attack London in G3.
Of course, the second time you do this your opponent will see it and build 9 inf in London on UK1. But then you just go after Russia!
I would think that most UK players will always start UK1 by counting the number of units germany can have for a G3 seaslion. Then buy 9 infs every time. (Unless germany for some reason lost its navy in G1 and the british one is intact)

6 inf 1 fighter is more common, as has been said elsewhere. It’s still strong enough on its own, and the fighter is far more flexible, especially UK 3+.
I only see/do 9 inf buys when Germany buys transports (plural) on G1, or if you’re super paranoid and Germany saves 30 G1.