Some of the users of HP41CL bought it with serial interface. They did it in order to be able to load new modules, I guess that many of them never did - it was too risky if you didn’t have the right instructions. At least this was my case - other users might have bee more experienced or daring.
Well, Monte Dalrymple has prepared a guide for the updating of modules in your calculator. You can find it here:
I have not tried it, but I plan to do it during these holidays. But for you users, it may be of help.