Stealing 3rd

No, that's not what that number means. 18-6 means good lead/not good lead, not steal 2nd/steal 3rd. In ARod's case a 2d roll of 6 means good lead (18), any other value means not good lead (6).

Stealing second is a (-2) adjustment if the runner is held.
Stealing third is a (-4) adjustment.
Stealing home is like (-9) or something.

No, that's not what that number means. 18-6 means good lead/not good lead, not steal 2nd/steal 3rd. In ARod's case a 2d roll of 6 means good lead (18), any other value means not good lead (6).

Stealing second is a (-2) adjustment if the runner is held.
Stealing third is a (-4) adjustment.
Stealing home is like (-9) or something.

From the advanced rules of Stratomatic for stealing third
"Stealing Third Base

An attempted steal of third base is slightly different. In order for the runner to steal, he must achieve a good lead, If the manager's dice roll results fail to fall within the attempt steal range of the would-be stealer, he may not attempt a steal of third base. Of course, the runner is out if the dice roll results fall within the out stealing range. If the baserunner achieved a good lead, roll the 20-sided die and refer to the SECOND rating number (14 in the example) of the potential stealer. Deduct -4 if the defensive manager had indicated that he was "holding the runner on", also take into account the catcher's throwing arm and the pitcher's hold rating,”

https://www.baseballthinkfactory.org/btf/pages/basesim/somrules.htm

You're taking the first number. This number is for the success steal of second base. The second number -6- relates to the chance of stealing 3rd.

ARod's chance would be:
6 good lead
+0 adjustment (not holding ARod)
- 4 Howard arm rating
+0 Bouton hold rating

2= chance to be safe.

For stealing second base there is a rule for getting a good lead, if you get a good lead you take the first number to begin calculations, if you do not you use the second - in AROD’s case the 6.

Thanks gkhd11a, you're right, I just didn't bother to explain all scenarios.

Bottom-line for 3rd base: If the baserunner achieved a good lead (for stealing 3rd), roll the 20-sided die and refer to the SECOND rating number. For ARod, this is 6.