Yes and no. The original Umbrella seals on these engine worked well enough. Most machinist and books I've read agree that what works oem is what should go back in there. Modifying, (positive lock), is unessasary unless the guides are so worn that oil usage is increased substantially, or one is going full on racing. Both umbrella and positive seals work very well on the 3.8.
The only drawback with umbrella seals was that they got hard and fell apart. With the newer technologies of Viton, the seals can go on for hundreds of thousands of miles w/o any issues. The cure before was the positive seal type requiring machining and more expense.
In my case I'm going with new bronze guide liners. That alone solves a lot of oiling problems associated with the 3.8 valve guide. So more machining just to install positive seals in all the bosses is an additional unnecessary cost.
But sadly, I've run into a brick wall. It seems that I can't find any Viton umbrella seals with a boss diameter of 500"-531". Most places I've looked only stock the positive type. These do work for my engine w/o any machining on the intakes but the exhaust will need machining if I do decide to use positive lock seals on the exhaust boss.
Then there's the additional cost of buying new exhaust valves w/o the oil step. Perhaps it would be foolish of me not to machine the exhaust bosses once the heads are out since I don't want to remove them again in the future if I change my mind.
But I am not completely convinced that one needs a seal on the exhaust boss. The oil step on the exhaust valve worked very well and no machinist has ever noted any issue or any drawback with this design. I know it was a cost saving design by Buick and I've read stories of blue smoke in the morning as a result of this. But I've never experianced this and I bet this blue smoke was as a result of hard and beat seals not a design flaw.
