Glazing Compound

Temperature of my south-facing windows probably ranges from 100+ Fahr. in the Canadian summer (air temps to the 90s) to -40 Fahr. in winter (air temps sometimes that low.) What is the most suitable glazing compound.
Conventional putty (mastic) seems to last no more than 5 or 6 years, even when carefully applied (onto timber dampened with linseed oil) and painted thereafter. The chap who restained the siding 3 or 4 years ago patched glazing with paintable latex caulk (25-year guarantee) but this did not last on south- facing windows.
There was a similar problem on the (cedar) windowsills which rapidly deteriorated in normal weather -- now cured by: 1. Filling with Dynamic brand Dyna Patch spackle compound, sanded glassy smooth. 2. Ten to 15 coats of stain (Pittsburg linseed-oil based). Every time the stain can is open, I add another coat. It builds up in time like enamel and becomes totally weatherproof. So I may try using this Dyna Patch as window glazing as well -- but would welcome advice from people who have solved this problem earlier.
Don Phillipson
Carlsbad Springs
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