Personally I don't think that if you will shoot with you PU sniper few times a month, something will happend with alloy scope in observed future.
I think this problem is exaggerated. Of course, steel scopes have more stronger construction, which is very important in war time conditions. But now is not war time. If this problem was so serious, there will be no way that 80000 of such scopes were issued, and we still could see them.
Alloy scopes are rare, but not unique, and many of them are still used. And anybody see that famous alloy powder at lenses?
Also, we should not forgot about Progress scopes with alloy rear lense block, many of them were issued in 1943 - beginning of 1944.
Krasnogorsk scopes has one advantage comparing to them - they have additional paper gasket inside rear lense block.
It's intresting, that when GRAU prohibit production of scopes with alloy details (only Progrees produce alloy rear lense block that time), Krasnogorsk already stoped production of their scopes. It mean that they stoped scope production not because they were too bad.
Most of the Krasnogorsk scopes that I was able to look inside, were covered with some reddish grease or varnish, which was still sticky.
Only one early unfinished (grey) scope have dark finish inside.
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So personally I prefer PU sniper with alloy scope - very intresting, rare, and progressive at that time item.