Window pane replacement
 

I am trying to repair a broken window pane but all the do it yourself info applies to wooden windows that use glazier points and putty. My windows are aluminum and the pane has what appears to be snap-on plastic molding around it. Most folks say that all you do is use silicone caulk around the frame of the window pane, set the glass in the frame on the caulk bead, and then snap in the plastic molding (after cutting it with miter corners). All the scuttlebutt is that this is an easy repair but I have a few questions about the details, and as we all know, the devil is in the details?

What I am unclear about are the following items:

1. How much clearance around the pane is required for the plastic molding to fit properly? Is it the same as recommended for wooden windows (i.e. cut the pane 1/8 inch shorter in length and width)

2. Is silicone caulk the proper sealant to use between the frame and the glass? The existing material, although nearly 20 years old, seems to have a tarry consistency and is black in color.

3. What actually holds the pane in place--is it the caulk or the molding or both?

Thanks for any help.

JoeHomeOwner