Never buy DLC at full price. Dovetail Games participates in massive Steam Sales every quarter (Summer, Autumn, Winter).
Valve (Steam) is not stupid. They have a heuristic detection system called "License Restriction Enforcement." Train Simulator Classic Dlc Unlocker
If you use a DLC unlocker:
Is it worth losing a $5,000 game library for a $19.99 DLC route? No. Never buy DLC at full price
The Train Simulator Classic DLC Unlocker is a software tool or patch that allows users to unlock Downloadable Content (DLC) for Train Simulator Classic without the need to purchase it through official channels. Train Simulator Classic, developed by Kuju Entertainment and published by Microsoft, is a popular train simulation game that has garnered a significant following. The DLC for the game includes new trains, routes, and scenarios, enhancing the gameplay experience. Is it worth losing a $5,000 game library for a $19
If you are frustrated by the "unlocker" culture, consider switching to Train Sim World 5. The graphics are modern, and the DLC model (while still expensive) offers a "Train Sim World Pass" subscription for $8.99/month, giving you access to everything without paying $5,000.