Plug-in dependencies

I was issued a new PC about a month ago and having a problem setting up a
plug-in I developed for Rational.

Old PC: Windows 7, RDi 9.6.0.4
New PC: Windows 10, RDi 9.6.0.6

The plugin was compiled on the old PC and has been in use for quite some
time, with enhancements added over the years and thru different versions of
Rational. It is also working fine on my new PC.

But now I want to make a change to it. I tried importing it as a plugin
project, and also tried creating a new plugin project, but in both cases it
cannot find the plugins it requires, namely org.eclipse.ui,
org.eclipse.core.runtime, and com.ibm.lpex. They are in the manifest but
with the red X saying they cannot be resolved.

Fortunately the old PC was not reformatted yet, so booted that up and
compared the projects between the 2 PCs for differences. The only thing I
can find is when I right click on the project, select Properties, go to the
Java Build Path entry, the Libraries tab, and under Plug-in Dependencies,
it shows 21 jars from the SDPShared\plugins folder including 3 that appear
to match the plugins above that I need. On the new PC it does not show
any. I don't ever remember adding them.

So I tried adding them on my new PC using the Add External JARs button. It
does add them to the list, but at the same level as JRE System Library and
Plug-in Dependencies, not as nodes under Plug-in Dependencies. That takes
care of the errors in the java source, but not the errors in the manifest
itself, which prevents it from compiling.

Any ideas if I'm looking in the right place? Or how to get those JARs
listed under Plug-in Dependencies?

Thanks!
Rick