NGK BKR6E vs. BKR6EY. What's the diff?

[Xristos Pronios]

OK people,

It's tune-up time for me and I start creating questions.

Changed plugs to std BKR6E. Old plug was BKR6EY. Anybody knows for sure what
is their difference???
Did the Nissan dealer that used the EY's f@ck&d up the type?

Checking the NGK part number codes, Y at the end means "V-grooved center
electrode (14mm only) 2.5mm insulator".
Now, BKR6E IS also v-grooved and 14mm thread diameter, so this leaves as a
difference the ALL important "2.5mm insulator".
Visually inspecting differences during the change left the impression that
the EY tip was actually a little longer than the plain E.
Anybody has any experience with both types?

BTW, the old plugs where in MINT condition, except signs of overheating on
(all of them at) the start of the insulator above(!!!) the 5/8' part (i.e.
outside the cylinder). If anyone has any idea I can post pictures. It may
have been some kind of oil residues but the problem was they seemed to
"emanate" from the base of the insulator upwards!

Chris
1992 Sunny 2.0GTi