The metal bell cap goes up and taper down, both sides the same. I'd definitely take it back to the shop and make them do it right to avoid premature failure. Upside down there may be an issue with clearances under maximum movement. Internally there are likely differences with the shape of the hydraulic chamber having more fluid at the top that may or may not lead to premature failure if the load forces are significantly different on the rubber body.

I'm pretty much convinced it has to be my front engine mounts. I'm not sure whether to blame myself for causing an old one to fail by jacking the tranny up at the front edge when I replaced the trans mount. I can forgive almost 30 year old rubber for getting hard and cracking. I'll replace both mounts, hopefully ending up with a good spare for the other 940. Last time I did red block motor mounts I supported the engine with a wood cross brace between the strut towers, lifting it a bit by the engine hook. It gives you full access underneath aand decent access above. This time I'll likely jack underneath at the front lip of the oil pan as per Matthew's.

For others following this thread, in addition to what's in the brickboard FAQ here, Matthew's Volvo Site has an excellent tutorial with pics on replacing the front hydraulic mounts, most especially cautions about lifting the engine too much and straining old hoses and the transmission cooler lines at the rad.

https://www.matthewsvolvosite.com/forums/viewtopic.php?t=37474

NLA in the Volvo parts chain, I'm now debating which brand to go for. Corteco (Freudenberg Group, Italy) and Feybe-Bilstein (France) are likely top quality OEM, both expensive and both seemingly hard to find in stock at the moment. I suspect Corteco may be OEM as Volvo often sourced seals from them, but they often also sourced from Bilstein. ProParts Sweden seems the most popular for decent quality. To the best of my knowledge, ProParts sources from other manufacturers, mostly Europe, but also global. FCPEuro sells them with their lifetime guarantee. URO, a branded divison of US based A.P.A. Industries, is another commonly available one, often cheaper and with a lesser reputation for quality. A.P.A. sources global, but may make some of their own rubber products. IPD just says "aftermarket" depending on availability, so could be any of those. RockAuto has numerous jobber quality brands of unknown quality as far as reviews go.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now