GMF Tooling support is provided by the community on a volunteer basis. You may use the following means to reach this community.
For frequently asked questions and known pitfalls please refer to the GMF FAQ. You might also consider the GEF Troubleshooting Guide,the SWT FAQs or the Eclipse FAQs.
Ask questions on the GMF Community Forum or the GMF newsgroup (same contents).
Report defects and ask for enhancements by creating a new bug entry in the Eclipse Bugzilla.