Needs to be countersunk.  My mechanic uses 3" fender washer AND a block of wood. 

Karl Wolz
Sent from my electronic umbilicus

On Jun 14, 2013, at 8:59 PM, JRodgers <jrodgers113@GMAIL.COM> wrote:

> Might do well with a block of wood between the old seal and the hammer,
> to even out the pressure of seating it.
> 
> John
> 
> On 6/14/2013 9:57 PM, Alistair Bell wrote:
>> I agree, use the thicker (and heavier one). GW sells an expensive thick one that by some accounts is the best. I have had 2, one purchased separately and one with a Victor Reinze kit. The latter was thinner and less substantial.
>> 
>> Drive in carefully, one can de-burr case hole a little with de-burring tool to remove sharp edge. Bottom the seal out, use old seal between hammer and new seal.
>> 
>> alistair
>> 
>> 
>> On 2013-06-14, at 6:54 PM, Jeff Lincoln wrote:
>> 
>>> Karl - that's what I installed the thicker one. I did counter sink it
>>> though per go ole' Boston Bob's video.
>>> 
>>> Why the thinner one? I picked the thicker one based on a big write up on
>>> the Go Westy site .
>>> 
>>> 
>>> --
>>> Thanks,
>>> 
>>> Jeff
>>> '85 GL (Gertie)
>>> '78 Bus (Melissa) Patty's Bus
>> .
>>