Hi
I said that I'd gotten to the stage of knowing that I've been beaten but apparently I hadn't. Further investigations uncovered the availability of a 5.2 inch (132 mm) 650 mm parabolic mirror and I have just ordered one from the States. I will also go back to Bunnings and get a length of 150mm storm-water PVC pipe which you may remember is the perfect outside diameter and begin my rebuild. It will be longer and heavier than the original tube but at about 650 mm hopefully not too heavy for my strengthened tripod.
I have also looked into the secondary size issue but I'd prefer not to go to the even further expense of a new secondary and holder. In any case, the new primary will have a focal length of 650mm and my calculations give a suitable secondary size of 36.5 mm. The similarly spec'd Skywatcher SKP13065EQ2 lists a secondary size of 34.5 mm which may or may not be the perfect size but is a similar result. I measure the Powerseeker 127 secondary size at 40 mm inside the beveled edges and given the fact that the primary mirror is slightly bigger (which I figure negates the effect of a slightly large secondary obstruction) and also the fact that I can only find 41mm or 32mm secondaries available on the web anyway I won't worry about trying to get things exactly right.
A second factor in my decision is that I've just got my new GSO 8" Dob and a 10:1 Crayford to go on it
so my Powerseeker will be relegated to 2nd / holiday scope status. Somehow the GSO and my design and build of a Equatorial Platform has assumed a higher priority for me.
Jarrod, if you are interested in pursuing an upgrade to your scope, I will be happy to let you know how I go but maybe don't do anything drastic until I know my results as I guess there is the possibility that this may all end in (more) tears.
Concerning your last question, I have no idea what to do with the redundant spherical mirror. If you can come up with something, let me know.
Steve