back in business - the Swiss Alps were worth a trip!
I tried suggested workarounds without any success. The tunnel stays locked for me and my mine wagon.
I did some googling with various search terms and finally the game name plus part of the save game file name led me to a german adventure game site "adventurespiele.net" where all the save games for this game were available in one zip file (Click here)
. Downloading from that site needs registering.
Their walkthrough also tells with highlighted letters that there is a bug in this game preventing entering the tunnel. Their walkthrough stops right before entering the tunnel and continues when Jekyll walks out of that tunnel. I just wonder whether they got their save game files to continue the game from developer or some other player who has successfully played through that part of the game, the story doesn't tell. Maybe this is Windows language dependent bug?
One of you with american (english) Windows could try using the save game files of chapter 3 act 2 to see if it works in such environment letting Jekyll to enter the tunnel.
The readme file in that zip package denies right to share the package outside the community without asked permission. Maybe your admins could cooperate with this matter to get it published by gameboomers as well?
My acute problem seems to be cleared now. Thanks for everyone here for your kind help!