Best glue for fixing broken parts

Blockwork_Orange

I was wondering if anyone had experience with gluing broken bricks or plates back together (either good or bad). 

What sort of advice or tips does anyone have to offer?  The parts I need to fix are some plates from a Legoland set from 1973.  

I know I can buy replacements through Bricklink, but I figured I'd try to restore the sets with the original parts as much as possible before I go that route.

Huw

MEK if you can get it, it's a solvent that the pros use.

The_Rancor

Kragle?

madforLEGO

If they are older LEGO pieces, maybe @Istokg or @LusiferSam can point you to a solution?

CCC

Which plates are they and how much do they cost to replace at BL. As unless it is anything hard to find, I wouldn't bother trying to repair them.

Astrobricks

In my mind, once a broken piece, always a broken piece even if repaired. Besides, I would expect repaired pieces to be very vulnerable to breaking again under clutch stress.

LusiferSam

Most adhesive cements for plastic models will work.  A majority of model kits are polystyrene, so adhesive cements meant for this will work with ABS.  They work by chemically melting the plastic together.  When done correctly the bond can be stronger than the original pieces.  MEK is often the primary ingredient is many of these.

Testors Liquid Cement for Plastics or Tamiya Extra Thin model cement are good choices and easy to find.  Personally I like Tenax 7R when building models, although I'm not sure if it is still being made.  It's been on and off the market a number of times in the last decade.  There are a few others out there.  I'd avoid any that come in a tube, like Testors red tubes.  They have thickeners that slow the drying time, but make the product stringy and a mess.  I only use these for small interior details where I need the time to adjust the fit and can hid errors or messes.

You don't need a lot of these kinds of cements.  A tiny amount applied along a near gap between the parts will fill most the joint via capillary action.  If you've never done this before, get a cheap model car or airplane and practice first.