I agree exactly with Spook's point.
The timing belt, front seals, and waterpump may not be worn out now; but by 150K, one or more of them are likely to fail. The service manager is right, that if the seals don't leak now, you don't NEED to replace them. But are they likely to make it another 5 years or 50,000 miles? Not likely, and then you'll be back. It's best to pay just a bit extra for the seal replacement, than to have to pay ALL the labor again for JUST replacing seals. Likewise the water pump is cheap insurance. The new seals, too will protect your investment in both the timing belt and the water pump- oil leaks attack rubber parts, causing timing belts to fail prematurely, and water pump top seals to leak badly, causing coolant loss.
Volvo will probably get about $10 each for the 3 seals (cam, crank, intermediate shafts) and about $95 for a water pump. I don't know what they get for the tensioner, but you could probably forgo replacement of it- I've seen very few of them fail. Not that it's impossible, and like the other items, it is cheap insurance against failure.
Just to note, I did recently (december) replace a timing belt in a 1988 240 that had failed due to leaking seals- the rubber belt was completely ruined by the oil, and the teeth stripped off it.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K