I'm currently replacing the seals in the front calipers but am having a very stressful time getting the piston back in, followed the gregorys manual instructions but have had not luck, resolting in a torn dust cover. can anyone suggest a way to get the piston back in and seal properly on the dust cover?
Car is ED.

What assembly fluid are you using? Is the piston seal in place properly? Don't try to force it in. With a decent assembly fluid, the piston will quite easily slide in.

Is it a new piston or the old one?

original piston, all new seals, have been trying for 3hrs now and still got no where, book says to fit seal into caliper and push piston through seal, that just doesn't happen, have to resort to a bit of timber and hammer to tap piston down, and the end result is a torn dust cover, even trying the opposite way put dust cover on piston and place into caliper bore it still won't seal against the groove in the bore

I take it the piston wasn't scored or marked at all?

I usually put the dust boot on last. I put the piston seal in the caliper, then spray a bit of assembly fluid on the external surface of the piston, and also inside the piston housing...

Slides right in, no dramas..

Then before I push the piston all the way in, I slide the dust boot over the piston, and push the piston down..all that's left then is to put the edge of the dust boot into its groove

the piston has to be like new,no pitting-chrome flaking-rust or damage,smooth as glass.the seal groove has to be clean,i use a tooth brush,clean the dust boot seal-if rusty,use a wire brush to clean it.make sure the seal is square and not twisted and use a assembly lube,the rest as above, i use 2 thumbs to push the piston in,if you cant use a g clamp to start the piston,its fiddely and you need to be cool,and carefull.use a old brake pad on the piston to keep it square when using the g clamp.

If your having that much trouble, get the exchange ones from Repco. Make sure you take your old ones with you, coz then you don't need a deposit.