In most cases, a character displayed as an unexpected ? is usually the result of using an incorrect NLS_LANG setting in the Forms environment. This would be set in the Forms default.env (or custom file if you created one). Also, generating the "X" files (fmx, mmx, plx) files in an environment that has NLS_LANG set to a compatible setting is also a good idea.
All that said, I am in the US, using a Win7 client (IE10 - JRE 7u51) and a default installation on Win2008, both with English language sets. I have no problem inserting or retrieving µ
You should probably consider checking the NLS_LANG setting. If that doesn't help the problem, I would recommend patching to the latest Forms and JRE version. Be sure to do this in a test environment before moving to production.
I don't think WE8ISO8859P1 is sufficient to support what you want. WE8ISO8859P15 or UTF8 or AL32UTF8 may be a better choice.
The database I tested with in my previous post is configured with AL32UTF8 and my Forms environment is using the system default settings as I mentioned.
Thanks for your feedback Michael.
I'll do a bit more testing.