help with a Ted Williams 799-190720

I just received a Ted Wolliams model 799-190720.  It was completely disassembled.  I got a hold of a cross section of a el- dorado 799-190721.  I have 2 questions:

1-I have heard these rifles have problems holding air, and I do.  I have changed all o-ring and I get the same weak pressure with 1 pump or 8.  Is there anything else I could try?

2-I also have two plastic washers that are flat on one side and rounded off on the other.  They are not on the cross section of the 799-190721 and i can't for the life of me figure out where they came from(which may be my problem #1?).  Everything else looks the same, but they may be slightly different. 

Any help would be appreciated.  Thanks.

The fella who gave it to me said he bought it around 1978.  The only markings are "Ted Williams Brand, Sears & Roebuck Co., Model 799-190720

Edited by PSI44

Just to add some info.  I tested it out some more this morning.  When it is pumped, it will put air pressure in the air chamber and hold.  When the lever is moved out to pump again, it looses the pressure.  Thats why I always have the same weak pressure.  It seems that the piston that lets the air into the air chamber won't hold.  This piston seats itself into a metal to metal seal.  I don't have any o-rings or gaskets to change here.  I am still at a loss and would appreciate any help. 

I checked out the 880 and it does look identical.