Window pane replacement

I am trying to repair a broken window pane but all the do it yoursel
info applies to wooden windows that use glazier points and putty.  M
windows are aluminum and the pane has what appears to be snap-o
plastic molding around it.  Most folks say that all you do is us
silicone caulk around the frame of the window pane, set the glass i
the frame on the caulk bead, and then snap in the plastic moldin
(after cutting it with miter corners).  All the scuttlebutt is tha
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 plasti
molding to fit properly?  Is it the same as recommended for woode
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 an
the glass?  The existing material, although nearly 20 years old, seem
to have a tarry consistency and is black in color.

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

Thanks for any help.

JoeHomeOwne

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JoeHomeOwner