Shredder's inability to find the Turtles Lair

[Icebot]

Originally Posted by Original TMNT Cartoon Fan

But not on his way back to the laboratory.

I think he left in a hurry and didn’t remember where the lair was later. After all, it was shown he still didn’t know where it was in later episodes:

Pizza By The Shred: he needed an anchovy homing device to find it and ended up in the Rat King’s domain.

The Missing Map: he needed the map to find the lair, ended up on a wild goose chase.

Also Baxter Stockman found the lair in Return of the Fly.