I agree with Randy. Our muffler systems may have minor leaks due to fitment issues at the pipe connectors, but at the header and downpipe it's more likely the installer doing something excessive, like wrestling the system around too much with the front muffler bracket unhooked and maybe also a broken bracket at the downpipe heat shield, such as when trying to disconnect or fully the pipe joints. There's also the possibility of the whole muffler system being hit from the rear, like backing into a low wall or high curb.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

The supply chain of the Starla exhaust system components for our 900s and other Volvo RWD is a chronic problem in recent years for all aftermarket suppliers and even Volvo. The Volvo parts chain is now Walker. Walker now owns Starla, a Swedish company, which adds to supply chain issues. Walker and ProParts Sweden listed exhaust components are Starla equivalents, possibly others. I'm not sure how many of the Starla/Walker components are still made in Sweden, which further complicates things if manufacturing is scattered around the globe.

You'll go through periods, often many months, where certain Starla/Walker components are scarce as hens' teeth, most recently the front muffler and the tailpipe as you note, also the oval rear muffler bracket. Complete kits are even more difficult to source. Even if you find all the individual kit components, they may be in separate regional warehouses, increasing shipping costs customers when fixed shipping costs aren't bundled for the entire order (RockAuto is such an example).

These days RockAuto is often your best source for "in-stock" Starla components when you can't find them from others, usually listing them as Walker. RockAuto is now my first choice supplier when looking for everyday parts and has been for years now. They have an increasingly good selection of OEM quality and Volvo OEM suppliers. They do not source Genuine Volvo like FCPEuro, IPD and a few others. FCP used to be my first choice until prices went up to help cover the cost of their excellent customer service, return polices, faster shipping and lifetime guarantees. Way back, IPD was my preferred supplier when they had the corner on Volvo aftermarket, but pricing and shipping costs have always been a killer, especially for me needing cross border shipping. Note that RockAuto does not offer free shipping or telephone customer support, but has a contact form that does work.

I'll mention a few other things here while I'm on the topic.

There other exhaust component brands out there, such as AP. Some are econo quality. Starla is only everyday quality, using standard double layer aluminized thin steel casings (rust soon starts between layers, eventually perforating, I recently peeled off 80% of a separated skin). Starla pipes are only medium gauge, which typically lasts 1.5 muffler lifetimes, all the more reason to replace the entire system. Walker makes various levels of quality, including premium flow-thru steel casings with a lifetime guarantee, but there is no Volvo 700/900 fitment listed. Amazon is a good source for both econo, everyday and stainless quality, but buying components one at a time of different brands can make shipping costs prohibitive and often create fitment problems.

Best to stick with the same brand to assure fitment, especially the over axle pipe, tailpipe and the oval rear bracket. Muffler shops have the advantage of using torches and pipe expanders, also custom making pipes, brackets and using universal fit mufflers when needed. When your back is against the wall, a local muffler shop can almost always figure out something for you. Whenever possible, use tapered split ring clamps (the type Volvo uses) that won't crimp a ridge into the pipes and make them difficult to separate later -why shops use torches. Good ring clamps that won't soon rust through are more expensive and often harder to find. Ring lamps aren't appropriate when you've got a fitment issue -why shops always use U-bolt clamps.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

I had this same problem a year ago with FCP. I got the front muffler from Rock Auto. Had a good warrenty
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89 240 wagon, 94 940, 300K, 94 940, 141K