I am replacing my chain with the recommended 630 non-O-Ring type.  I want to clean out the sludge from the chain case.  I have the chain case out and removed the o-ring seal to prevent damaging it, but it only opens about 1/4 of an inch, 6-7 mm.  I am reluctant to pry on it more for fear of damaging or breaking it.  Could the resistance be from the seals and I just have to pull it apart harder?  The service manual just says 'open it' without any specific technique or steps.
Any ideas?
Happy New Year from the West Coast of the States!

Hi Grandparipper,

...I'm having trouble understanding your description, ... photo??
The cover can simply be lifted off parallel to the side (provided the chain is removed).
If it only lifts a few millimeters on one side, you've forgotten a screw.

Regards, Bruno 8-)

Hallo Grandparipper,
ok, you have deinstalled the Chain competely?
you have deinstalled the rear Chaincover from the rear arm?
you have take out all screws from the cover plate?

Then it shout be possible the seperate the cover plate from the housing.
Sometimes it is possible the the old O-Ring will give you a little bit off resistant, anyway, be carefully.
Perhaps, add a little amound of WD40 or similar stuff and let get in for a while.

In the End it is difficult to get spare parts.

Kind regards
Anja

Thank you, Anja.
Yes, the chain was cut and removed.  The rear chain case is off the bike and the perimeter screws are all removed.  The o-ring seal around the outside of the case is out also to prevent it getting damaged.  The 2 halves can be pried about 1/4 inch or 6mm, then it feels stuck.  
I think it is the inner seal deforming slightly or losing flexibility after 45 years.  (Like me perhaps?)
I just wanted reassurance that a little more pressure is needed and that I have not skipped a step.
I think I need to apply wedges around the perimeter evenly, then gradually tap them in until it lets go.

Good Day Grandparipper,
could it be possible, that you can post Photos of the chain cover?
To get a real impression of the object where we disscuse about., Photos are mostlty good helpers.

Regards Anja

Hello Grandparipper,
short Question: do you could open the Chain Cover, meanville?

Regards
Anja