Ultimately its your decision. I have Seafoamed many cars without issues including all of mine. Some had noticeable differences and some it was negligible.
If you use it correctly there shouldn't be a problem. It very well could have been a pre-existing problem that Seafoam helped him find sooner than later or it was done incorrectly. I've seen problems with people taking the brake booster tube and sucking it straight out of the bottle with it… DON’T DO THIS! You could cause hydrolock, which is unlikely but possible or blow a head gasket from too much pressure from the liquid in the combustion chamber.
Warm the engine up, open the bottle and slowly POUR the seafoam into the brake booster vacuum line, it will rough idle (vacuum leak) you could have someone hold the RPM at around 1500 or so. When you put 1/3 into the manifold reattach the brake booster and shut the car off for about 10-15 min. Come back and it will rough start/idle, rev the crap out of it and it will give you a nice smoke show. When it starts to clear up a little take it for a 20min or so hard drive. This has always worked for me.
I would do some in your oil when the time comes and some in the gas now. If you are really worried you could skip putting it in the intake manifold.
