110 Brake Calipers

I have an exMOD Defender 110 with vented discs in the front and solid discs in the rear.

Would it be better to rebuild old calipers with stainless steel pistons and new seals, or purchase new AP-Lockheed calipers and save on the rebuild time/hassle?

These seem to be quite reasonable from Paddocks:
http://www.paddockspares.com/seb500470g-front-brake-caliper-new-lh-vented-from-la930456-ap.html

Thanks

WEhy do you want to change them?
If they are OK, leave alone, but if they leak or are siezed, I'be be inclined to replace with new.

Unless the pistons are pitted don't change them.
Clean up & put back on.

If pitted do full rebuild & replace all seals. Don't buy new calipers most are crap.

My vote is for split them, and rebuild with new seals and stainless pistons. But that is only if there is a problem with them currently. Otherwise as said if they are fully working just clean them up and refit.
If you do this make sure you get new gallery seals (I can dig out where I got mine if needed), and only use genuine seal kits. I ended up building mine twice as the new aftermarket seals started leaking about a month later. Not been a problem since.