Josh, there are no old VW parts or cars in Mexico. All the old ones were used up, rebuilt, used up, rebuilt, used up........ To death.
Didn't find any diffs in Monterrey. No Type 181s is the reason I think. I didn't see a single 181 in Monterrey. At the north end of town, all the junk yards are in one place. You can park your car and walk to all of them. They call it the junk yard mall!
So from there, I headed west to Mazatlan. I took the super twisty road from Durango to Maz. To give you an idea how tight it is, I counted turns. 290 turns in 31 km. I would have set up the camera for a video of how tight they can get, but it was dark out. The turns were so tight that when oncoming transports put their outside wheel on the white line, the rear axle of the trailer is 3-4' in MY lane.