Topband: KT34 & Shunt Feeding

[Phil - KB9CRY]

I've got to drop my KT34XA to upgrade the element to boom adapters (one 
of the original KLM version has become loose and will be upgraded with 
the DX Engr. type) and while it's down I want to perform other mods 
(it's already been upgraded with the M2 upgrades).  Anyway, this antenna 
is on top of a 72 ft. Trylon self supporting tower, which two years ago, 
I began shunt feeding on 160M.  That has worked like a champ but I'm 
concerned that the high voltages have been messing something up with the 
antenna.  Since the last year or so, I've noticed that the antenna seems 
dead on 10 & 15M.  I've verified it's an antenna problem by switching in 
the backup radio.  Front to back and SWRs on those bands are still OK 
but it just doesn't hear well; everything seems attentuated.  20M seems 
OK.  So, I have a few questions for the group:

1.  The original KLM 4:1 balun is a voltage type, correct? 
I'd like to change this out to a current type.  I know some folks who 
are using the Radio Works replacement with good success.
Can I make my own out of ferrite cores and using an impedance matching 
system (dual 50 & 75 ohm coax)?
Exactly what type & material cores should be used?
To what frequency is the matching system sized for since it's a multi 
band antenna?

2.  Can my attentuation problem be caused by the high voltages of the 
shunt feed messing up the balun?
When I did my annual inpection up top last summer, I did not notice any 
damage to coax, the element to boom insulators, etc.

3. The KLM has elements which are insulated from the boom.  I've read 
previously that one can place an impedance jumper (?) between the 
element and boom to prevent high voltage arcing at the insulators.  
Please tell me exactly what to do here.

Any other suggestion would be appreciated.  Tnx in advance, Phil  KB9CRY